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Transparent plastic preforms are essential for companies that manufacture goods like beverages, edible oils, and intermediate chemicals like alcohols and glycols to form the container for the end product. The color of these preforms is equally vital, helping determine the final product's appearance and its impact on consumers' acceptance, buying decisions, and perceptions of quality. 

Beyond influencing your customers, color consistency keeps manufacturing costs under control, since alterations can lead to waste. All cement the importance of color measurement at every stage of production to uphold quality assurance (QA) throughout the supply chain, from raw materials to finished goods.

The Challenges With Color Consistency in Transparent Plastic Preforms

Multiple factors can impact the appearance of transparent plastic preforms, from raw material variations to processing conditions and physical characteristics. All present specific challenges to overcome to achieve consistency and the desired appearance.

Variability in Raw Materials

Variability in raw materials is a frequent challenge for every plastics manufacturer, as well as producers who rely on plastic preforms.

Global regulatory bodies and consumers are embracing sustainability, leading to higher demand for the inclusion of more recycled polyethylene terephthalate (rPET). With this rising expectation comes new challenges, since rPET often contains high amounts of optical brightening agents (OBAs) to overcome yellowing. Every delivery of raw materials typically differs in that composition, making color measurement crucial to managing rPET variations successfully. Quantifying color at this stage empowers scientific, objective, and data-driven decisions to uphold aesthetics, quality, and performance.

Other challenges include variations in the amount and type of additives and pigments that can influence the final color. Additionally, contaminants like dust or residual color from previous runs may lead to alterations in appearance or clarity.

Physical Preform Properties

Transparent plastic preforms naturally present measurement challenges due to their physical properties.

Preform shapes and specifications represent the first difficulty. Contoured surfaces and variations in thickness inherently impact cooling rates, which can lead to alterations in color consistency. Inaccurate sample presentation can further influence measurement accuracy.

Additionally, transparent plastic preforms are susceptible to haze that affects color perception. This cloudy appearance is often caused by microparticles embedded within the plastic, which causes light to scatter when it interacts with the sample.

How Spectrophotometry Addresses the Challenges

Spectrophotometry is the most accurate and objective way to quantify color in transparent plastic preforms. Top-rated spectrophotometers solve the issues of manual visual evaluations — observer fatigue, error-prone assessments, and variabilities in surroundings that can affect how we perceive appearance.

Specialized Design for Transparent, Contoured Surfaces

This equipment provides scientific, numerical color data through specialized optical geometries and controlled lighting by measuring transmittance — the intensity of light at specific wavelengths within the visible spectrum that passes through the sample. Operators can then compare the readouts against established scales and indices, such as the Yellowness Index, to ensure the preform falls within acceptable tolerances, promoting consistent and repeatable results.

Higher rPET Content Without Guesswork

Tight color control with spectrophotometry is also how brands increase rPET without sacrificing appearance. When you have objective color data within seconds, you can raise recycled content while protecting appearance. Capture color measurement during incoming to set OBA dosing from data, not estimates. Using the same approach for in-process assessment and final inspection also helps identify alterations faster to uphold your quality control (QC) and support color consistency, even across different sites and suppliers.

Polyethylene terephthalate (PET) preforms are essential to attractive, durable packaging for industries like beverage manufacturing, edible oils, and more. As the market continues to grow, so does the need to accurately and objectively quantify appearance to uphold product quality. Spectrophotometry is the best solution for scientific color measurement, eliminating the error-prone nature of manual visual assessment for higher confidence and precise data. Explore why color matters in preforms, the challenges of color consistency, and the ideal equipment for measurement to ensure high-quality results.

Why Color Matters for Plastic Preforms

Color plays an instrumental part in conforming to standards, protecting products, and influencing consumers.

Industry Standards

Plastic preform color is vital in meeting industry-specific standards. Sectors like pharmaceuticals and beverages often have strict color tolerances to ensure safety, traceability, and regulatory compliance. For example, specific packaging colors may indicate the presence of certain additives or differentiate between product formulations. Adhering to these color standards helps uphold product integrity and consumer safety.

Product Protection

Some goods, such as certain pharmaceuticals and beverages, are sensitive to ultraviolet (UV) light. Ongoing exposure to UV rays can cause degradation, affecting visual appeal, medical efficacy, safety, or taste. Opaque plastic packaging forms a shield against UV light, helping protect the product within against excess exposure. Inconsistent color may signal uneven distribution of colorants or UV-blocking additives, potentially increasing the chances of UV rays penetrating the packaging.

Quality Perception

Products like edible oils and beverages compete in crowded marketplaces. As a result, standing out on the shelves is key to your success. The plastic colors you choose help attract attention and reinforce your branding with consumers. When your color remains consistent and appealing, it indicates your commitment to quality and meeting your customers' expectations. Conversely, color alterations can signify issues with your quality control or manufacturing processes, causing consumers to reach for a competitor's product instead.

You spot a batch of roasted cashews and think they look perfect—but the flavor testers disagree, and shelf life is inconsistent. If your QA team relies on visual checks, you’re working with blind spots. Inconsistent roast color means wasted product, unhappy customers, and lost revenue.

Here’s how two tools from HunterLab—Aeros and SpectraTrend HT—help you hit your color targets every time, keeping your QA process tight, efficient, and repeatable.

From Raw to Packaged: Where Color Can Slip

Let’s walk through a typical cashew roasting process. Color issues can pop up at any point.

1. Preparation – You sort and clean kernels, then adjust moisture to 5–7%. Too much water = pale roast; too little = fast browning.
2. Optional Blanching – You steam to remove skins, then dry back to 5%. Inconsistent moisture here skews roast uniformity.
3. Roasting
4. Cool & Season – Improper cooling affects final appearance and texture.
5. QC and Packaging – Visual checks and moisture tests help, but they miss subtle color shifts until it’s too late.

That’s where objective color measurement makes the difference.

Modern consumers have endless opportunities to choose products from your competition. Product consistency matters, and a visual inspection is no longer enough to gauge it. To appeal to the most discerning customers, your products need a precise, uniform appearance — and you need an accurate color measurement tool to ensure that's the case.

The Benefits of Spectrophotometers

Spectrophotometers measure light transmittance or reflectance from plastics, foods, drinks, and other materials. They eliminate the guesswork of visual evaluations and variable observation conditions, such as lighting, that affect the way we see color.

Using a spectrophotometer enhances a brand's identity by associating specific colors with its products. Inconsistent coloring can confuse consumers, leaving them more likely to choose a competitor's option over yours. The more consistent your products are, the more likely a consumer is to stay committed to your brand.

The human eye can perceive millions of colors, but it does not always distinguish them accurately. Two slightly different colors may appear the same, or identical colors may look different depending on viewing angle and lighting. This creates challenges when communicating about color. For designers and manufacturers, the inability to precisely identify and communicate color complicates efforts to replicate standards and detect discrepancies.

To reproduce an exact color consistently, manufacturers and designers rely on ways to quantify a color's properties and calculate the numerical difference between colors. CIELAB, or CIE L*a*b*, is a device-independent, three-dimensional color space that measures and compares all perceptible colors using three values. In this space, numerical differences correspond to the degree of change humans can perceive.

CIELAB is based on opponent color theory showing that the brain interprets retinal inputs as differences between light and dark (lightness) and between opposing pairs of colors: red/green and blue/yellow. This is known as the principle of color opposition correlation, as a color cannot be both red and green, or yellow and blue, simultaneously. For example, you will never see a "greenish red.

What Is the CIELAB Color Model?

The L, a, b color space was first defined in 1942 by Richard S. Hunter, founder of HunterLab. Hunter’s system used coordinates labeled L, a, and b, calculated from the CIE 1931 XYZ color space, and was intended to be more perceptually uniform. In 1976, the International Commission on Illumination (CIE) created the CIELAB model as a refinement of Hunter’s work. To distinguish between the two systems, CIELAB uses L*, a*, b* notation. The “CIE” refers to the French name of the organization: Commission Internationale de l'Éclairage.

Both Hunter L, a, b and CIELAB (L*, a*, b*) are grounded in Opponent-Color Theory, which assumes that the human eye perceives colors in opposing pairs:

• L scale: Light vs. dark, with low numbers (0–50) indicating dark and high numbers (51–100) indicating light.
• a scale: Red vs. green, with positive values indicating red and negative values indicating green.
• b scale: Yellow vs. blue, with positive values indicating yellow and negative values indicating blue.

An ideal color scale would be uniform, meaning that a one-unit difference would appear visually equal regardless of hue. In practice, neither Hunter L, a, b nor CIELAB is perfectly uniform. Hunter’s scale applies a square root function to Y/Yn for calculating lightness (L), which tends to compress values in the yellow region and expand them in the blue region. CIELAB, by contrast, applies a cube root function to X/Xn, Y/Yn, and Z/Zn, with a linear extension near black. While this improves uniformity overall, CIELAB tends to over-expand the yellow region of color space. Both scales are effective for measurement and for setting tolerance standards. However, CIELAB generally provides a closer match to visual perception. With practice, either system supports intuitive understanding and communication of color values.

What if your next plant-based drink could achieve stunning golden color—naturally, consistently, and without compromising shelf life? That vision just moved closer to reality.

A peer-reviewed study in Food Frontiers reveals how a one-step pH infusion of raw turmeric into soymilk delivered reliable, vibrant color. Using the HunterLab ColorFlex EZ spectrophotometer, researchers tracked L*, a*, b* values to evaluate and confirm the consistency of this natural process.

Please note: the ColorFlex EZ has now been upgraded to the ColorFlex L2. For a seamless transition and added benefits, you’ll find more details in the second half of this blog.

Key Findings from the Study

This study offers compelling evidence for a practical, clean-label solution:

• 94% curcumin transfer from raw turmeric into soymilk, with stable particle size and charge
• Both curcumin–soymilk and turmeric–soymilk showed b* increases above 40 units versus plain soymilk, creating a distinct golden-yellow hue
• Both freeze-dried curcumin–soymilk and turmeric–soymilk powders remained stable over a 30-day storage period at freezing temperature.

These results highlight how tristimulus color measurement enables effective monitoring of natural pigment integration across product lifecycles. More importantly, they demonstrate a path to achieving natural color in plant-based milk—a key priority for brands focused on clean-label innovation.

Why It Matters to HunterLab Customers

For Plant-Based Beverage Producers

The study provides a scalable route to functional pigment delivery. Use ColorFlex L2 to maintain color consistency across shelf life with simple benchtop quality control.

For Turmeric and Spice Processors

Validate raw turmeric batches without requiring purified extracts. ColorFlex L2 readings enable quick grading and premium positioning for buyers.

For Nutraceutical Brands

Support label claims of protein and curcumin co-delivery. Tristimulus color data confirm dose uniformity in ready-to-mix formulations.

For Food Science R&D Teams

Leverage a peer-reviewed protocol pairing pH encapsulation with tristimulus tracking. Reproduce or expand for other botanicals.

For Quality Labs and Co-Packers

Color shift is a primary indicator of curcumin degradation. Use ColorFlex L2 for quick pass/fail metrics before packaging.

Export buyers notice inconsistencies—do you? Manufacturers often rely on ground samples and handheld chroma meters. This method fails to capture whole-nut appearance. A roast-level measurement that aligns with consumer expectations can elevate product consistency—especially for global export markets.

A slightly over- or under-roasted cashew can affect perceived quality, flavor, and brand trust. Yet many processors still rely on outdated, destructive color checks that don’t reflect what the consumer sees.

Let’s fix that.

Why Color Accuracy Drives Cashew Quality

• Consumer confidence: Global buyers expect golden-brown uniformity. Irregular batches erode trust.
• Export readiness: Color variation is a top rejection reason for U.S. and EU-bound shipments.
• Flavor & texture proxy: Roast color is linked to browning index and sensory qualities.

The Problem with Ground Sample Methods

1. Inaccurate representation: Grinding mixes inner and outer nut layers, masking true surface color.
2. Prep variability: Operator technique affects grind consistency and packing.
3. Low throughput: Each test can take 8–10 minutes—including warm-up, grind, and tray prep.
4. Wasteful: Ground samples can’t be reused—costing time and raw materials.