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Color tolerances set acceptable limits for the appearance of a product and are an essential part of quality assurance and quality control processes for color. You can efficiently determine whether a product falls within the limits by establishing tolerances. If it does, the product passes. Failed goods fall outside the tolerances, meaning process adjustments may be necessary to create the desired appearance. 

Many industries, such as food, plastics, and chemicals, rely on accurate appearance. Tolerances enable you to establish a standard and decide how much variation to allow, giving you consistent color outcomes. 

What Is Color Tolerance?

Color tolerances are the parameters within which a product's color can vary yet remain acceptable. Typically, visual assessment is the initial step to define the acceptable color range. Spectrophotometry then objectively and scientifically quantifies and manages those tolerances.

Before establishing tolerance values, you must decide on the observer, choose a color scale, such as Hunter L,a,b, and then select illuminants for comparison, like D 65 and Illuminant A. Depending on what you're measuring, the scale you choose might come from the International Commission on Illumination (CIE), which sets global measurement standards, or from another entity. 

Once you have a comparison standard, you can gather products and measure their color to determine acceptable variations called tolerance values. 

In this process, you start by selecting a relevant standard for your product, then determine how much this standard can vary before it creates visible differences in appearance. This test helps you set boundaries for future production to objectively decide whether products fall close enough to the original standard to conform to quality expectations.

Detecting Color Differences

You can establish tolerances based on two levels of difference:

• Minimum perceptible difference: A visual comparison shows a just-noticeable difference between the standard and the sample. 
• Maximum acceptable difference: The level represents the largest acceptable difference between a standard and a sample. 

Focusing on the maximum acceptable difference means a broader range of acceptable values, while relying solely on minimum perceptible difference can lead to high rejection and material waste. As a result, choosing the right approach is typically industry-driven. For example, the food industry frequently uses the maximum acceptable difference, but pharmaceutical manufacturers usually opt for the minimum perceptible difference.

Range of Tolerance Definition

The range of tolerance is the acceptable level of variation related to an established color standard. You will establish this standard using a measurement model like CIE L*a*b*, which results in three values measuring:

• L*: Lightness, from dark at zero to light at 100.
• a*: Position on the red–green axis, with the positive number indicating red and the negative indicating green.
• b*: Position on the yellow–blue axis, with yellow represented as the positive and blue as the negative.

Once you establish a standard, you can decide on each dimension's tolerance. Here are the formulas for determining the difference (∆) between a sample and a reference:

∆L* = L*sample - L*reference

∆a* = a*sample - a*reference

∆b* = b*sample - b*reference

You can also calculate the total color difference across the three values in a single formula, with the results represented by delta E* (∆E*). Here's the formula to determine ∆E*:

∆E* = √((∆L*)2+(∆a*)2+(∆b*)2)

While ∆E* values can be helpful, use this method carefully. When the difference is spread over three dimensions, you may get a value that looks acceptable but has significant variation in one measurement, such as red vs. green. 

This variation will create a noticeable visual difference but may not impact the delta E* value if the other dimensions are close to the standard. If you calculate the difference values separately, you can more closely monitor each one to verify that none stray too far from the standard. 

Color is one of the first sensory processes humans experience. It can alert us to potential danger, like the orange of a safety cone, or tell us what flavor we might expect from a piece of candy.

Long-term changes to color appearance can have negative impacts — a dusty pink fire engine isn't going to draw attention as effectively as a bright red one. Learning about color stability and understanding its importance, challenges, and the best way to ensure it can help you prevent unwanted deviations from the intended, expected, and desired results.

Defining the Stability of Color

In its simplest terms, color stability refers to how well a material can maintain a consistent color throughout its life span. 

It's important to note that color stability substantially differs from color consistency and constancy. While maintaining those traits is also vital, these terms refer more to eliminating chromatic variations across batches, production lines, facilities, and observation conditions like illumination.

Factors That Can Impact Color Stability

Multiple factors can cause alterations in chromaticity as time passes. As a result, changes can arise during any manufacturing stage and throughout material storage and distribution. Excess exposure to the following can impact color stability:

• Moisture
• Oxygen
• Light and UV rays
• Extreme temperatures
• Chemicals

The Importance of Color Stability

Maintaining color over time is vital for several reasons.

Quality

Color and quality are inherently intertwined. Chromaticity that meets a consumer's expectations encourages them to form a positive brand image. When color conforms to industry standards, it also showcases your company as one committed to best practices. Color stability helps support these outcomes by ensuring long-lasting durability, which boosts perceived value.

Safety and Compliance

In many products, color stability goes hand in hand with safety. Consider goods like reflective safety tape, camouflage military uniforms, and edible oils, where color alterations over time can impact visibility or indicate potential contamination that would make it unsafe for consumption. Additionally, products whose color maintains acceptable tolerances in highly regulated industries prevent unnecessary fines or penalties.

Appeal

Customers may see color as the primary determinant in their purchasing decisions for certain items, like vinyl siding and roofing shingles. Remodeling a home exterior is a significant investment that consumers expect to last for years. Customers don't just want it to look good now — they want to know the color they see at first is the color they can expect it to stay, even after long-term exposure to the elements. 

Color surrounds us every moment of our lives and affects our emotions, behaviors and beliefs in large and small, conscious and unconscious ways. Color can set a mood, warn us of danger, give us critical information and even bring us joy. Despite the universal presence of color, describing it remains elusive, in part due to variations in color perception from person to person and in part due to a lack of descriptors for each of the millions of shades seen by the human eye.

Instrumental color measurement moves beyond the limits of human perception and vocabulary and allows us to capture color information as objective data, creating a common language of color that is essential for communication within and between industries around the world, ranging from food and beverage to pharmaceuticals. The two most advanced color measurement instrument types are colorimeters and spectrophotometers, both of which use sophisticated technologies to accurately and precisely quantify and define color.

While closely related, these instruments have unique qualities that may make one more suitable than the other for a particular type of measurement. Understanding the characteristics of a colorimeter vs. spectrophotometer can help you select the best tool for your application.

What Is a Colorimeter?

A colorimeter is designed to perform a type of psychophysical sample color analysis, which means its measurements correlate to human color perception. In other words, it is designed to see color the way we do.

Its results are direct and read as tristimulus values. A tristimulus value is one that identifies a color with characters that represent different dimensions of its visual appearance. A tristimulus value may contain values like X, Y and Z or L, a and b. The “gold standard” for tristimulus colors is the CIE Color System, developed by the International Commission on Illumination — the CIE in the title stands for the French version of their name.

There are a few unique components involved in a colorimeter.

• Illuminant: The illuminant represents a specific light source, such as daylight or incandescent light, to project consistent brightness onto the object. In a colorimeter, an illuminant is fixed.
• Observer: The standard observer offers a specific field of view with which to analyze the colors. A colorimeter usually uses a 2-Degree Standard Observer, which is suitable for color evaluation and quality control.
• Tristimulus absorption filter: The absorption filter isolates specific wavelengths to be applied to the sample.

Types of Colorimeters

Colorimeters are essential in determining color objectively and accurately. Their different varieties measure color to varying depths and degrees. Types include:

• Densitometers: These measure the darkness level, or density, of semi-transparent material.
• Photometers: Color photometers measure how color is transmitted and reflected.

How Does a Colorimeter Work?

A colorimeter’s usage is often based on the Beer-Lambert law, which tells us that the concentration of a solute is proportional to its absorbance. The colorimeter starts with a simple light source. With the help of a lens and tristimulus absorption filters, the beam of light becomes a single, focused wavelength which then moves through to the sample solution. On the other side of the solution is a photocell detector that identifies how much of the wavelength got absorbed. The detector is connected to a processor and digital display that offers a readable output of the results.

Now that you know how it works, let’s take a look at the pros and cons of a colorimeter.

In the past 100 years, the amount of food coloring used in food has increased drastically. This shift is due in part to manufacturers’ growing emphasis on making food look more appealing, last longer and attract as many consumers as possible. The U.S. Food and Drug Administration (FDA) imposes strict regulations and standards for the approval of artificial food dyes and how food producers and manufacturers are permitted to use those dyes in their products. Learn more about food color standards established by the FDA, including what technology your business can use to operate within regulation.

What Is Food Coloring?

Food coloring and food dyes are chemical substances used to alter or enhance the appearance of a food product. Three color additives make up 90% of all used food dye — Red 40, Yellow 5 and Yellow 6.

Using color additives or dyes is not a new technology. Natural food colors were used to color wine as early as 300 B.C. Early dye experimentation included naturally occurring color found in some spices and metal oxides, like saffron and copper sulfate.

The first synthetic organic dye — called mauve — was discovered in 1856. Mauve was the first of many discovered synthetic dyes produced via coal processing, earning them the title “coal-tar colors.” Federal regulation of color additives began a few decades later, in the 1880s.

What Is Food Coloring Made Of?

Artificial food coloring is derived from petroleum. There are three possible classifications for a food dye:

• Straight colors: Straight colors are free from most impurities and have not been mixed or chemically altered with other substances.
• Lakes: Lakes are the product of a chemical reaction that takes place after combining a straight color with precipitants or substrata of things like alumina, titanium dioxide and zinc.
• Mixtures: Mixtures are made by combining a color additive with another color additive or a non-colored diluent, which produces no chemical reaction.

When it comes to the appearance of color, you cannot underestimate the importance of lighting. Yet, lighting can be confusing, as much of the terminology sounds similar but has vastly different meanings. For example, two of the most widely used terms — luminance and illuminance — can be easily misunderstood and mixed up. Since lighting is an essential component of color, we’ll discuss luminance vs. illuminance below.

What Is Luminance?

The definition of luminance is the amount of light emitted, passing through, or reflected from a surface. Think of a lamp shining in a dark room — luminance would describe the amount of light passing through the lightbulb.

The meaning of luminance is often used interchangeably with the term brightness. However, when it comes to luminance vs. brightness, these descriptions are not interchangeable. Luminance is a quantifiable, measurable characteristic. Meanwhile, brightness cannot be objectively measured — it can only be perceived. We recognize that a light source is bright or dim, making brightness the visual sensation by which we become aware of differences in luminance.

We measure the luminance to account for the human eye's sensitivity to different wavelengths of light. We can then provide a measurement that correlates with human perception of brightness.

When it comes to color decisions for your business, luminance can also describe a certain color’s perceived brightness. Fields that often use luminance measurements include electronics sectors responsible for designing display technology such as screens and digital signage. The automotive industry also uses it for lighting and road safety purposes. Generally, products that need to be created for the comfort and safety of human vision will ensure luminance measurements are within the necessary guideline parameters.

Every object we see has color, and it is an essential part of how we interpret the world. But color isn’t an inherent quality of the objects in front of us. Consider a classic red apple. If you look at it under a blue-tinted light, it will appear somewhat blue, and if you look at it under no light, you won’t see anything. So, what color is the apple?

As it turns out, color is simply a perception of energy and specific wavelengths of light that reach our eyes. It can also vary based on the biology of a person and how their brain receives signals, so two people may not see an object as the exact same color. Let’s take a closer look at what color actually is.

Why Does Color Matter?

Color does more than make something red, blue, or pink. It influences our perceptions and moods and plays a significant psychological role.

A warm-toned photo feels uplifting or joyful, while a cool one is serene or depressing. We see specific colors as eye-catching— some may spur us to purchase. Think about your favorite brands — their logos and imagery are carefully selected to incite specific buying habits and make you associate particular traits with the company.

When it comes to products, color can make us more attracted to an item. Bright candies are colorful and fun, while a ripe red tomato may look remarkably fresh and juicy. Many manufactured products must maintain the same color throughout production to increase buyer confidence or improve identification. For instance, each pill of a specified drug must match the previous one, and each can of paint should be mixed to the expected color.

The psychology of color perception is an integral part of our everyday lives.

Isaac Newton conducted several studies using light, which led to the discovery of the rainbow. He found that passing white light through a prism gets refracted into many hues. White light is not white — it has the ROY G BIV sequence. In other words, the colors of our rainbow make unseen light visible. It is, therefore, apparent to the human eye.

The various wavelengths of each hue in the visible light spectrum account for the rainbow colors' arrangement, represented by the letters ROY G BIV. Thus, the longest wavelength is red, which has a wavelength of around 700 nm, and the shortest wavelength is violet, which has a wavelength of about 380 nm. As a result, as the various colors exit the prism, they fracture at a certain angle, producing a rainbow of hues.

While pioneering the concept of a light spectrum, Sir Isaac Newton divided it into seven colors, including indigo. This inclusion stemmed partly from the cultural significance of indigo as a prevalent dye at the time. Interestingly, the categorization of color is subjective and culturally influenced, with human perception grouping a continuous spectrum into distinct bands for easier comprehension. Newton's choice of seven colors was also likely influenced by the prevailing belief in the significance of the number seven.

The seven colors of the rainbow are:

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

Each hue is distinct in terms of frequency measurements and the values and meanings that society assigns to it.

Frequency and Exact Color Measurements of the Rainbow

Light travels in waves— its frequency is the number of wavelengths passing a given point each second—a shorter wavelength results in a higher frequency and vice versa. Humans can see light between 400 and 700 nanometers (nm) — the visible spectrum. Because each color has a different wavelength and frequency, each light color separates and becomes visible when passing through a prism.

The ROY G BIV wavelengths are as follows:

• Violet: 380 to 450 nm
• Blue: 450 to 495 nm
• Green: 495 to 570 nm
• Yellow: 570 to 590 nm
• Orange: 590 to 620 nm
• Red: 620 to 750 nm

What Does the Order of the Colors of the Rainbow Mean?

The rainbow's color order is ROY G BIV. Red has the lowest frequency at the top of the arc, and violet has the highest frequency at the bottom. When light passes through a prism, it refracts the different colors in the same order because each wavelength bends at a unique angle.

Though the order of the colors will always be the same, the way the spectrum is defined has changed over time.