How plastic containers get their color
Most colored containers and storage boxes are made from natural resin mixed at the machine with a small proportion of masterbatch: concentrated pigment carried in a compatible resin. The plant sets a let-down ratio, the share of masterbatch in the mix, and the color of the part follows from the pigment, the ratio, the base resin and the processing conditions. Some parts use pre-colored compound instead, where the color is mixed in by the resin supplier. Thermoformed takeout boxes take their color from the sheet, which is extruded with masterbatch before forming.
In this range the common colors are simple: clear, black base with a clear lid, white, and the natural beige of starch-based containers. Storage and organizer lines add brand colors, pastels and translucent tints. Each of these behaves differently when something in the mix changes.
What makes color drift
Masterbatch lot and supplier
Two lots of the same masterbatch grade can differ slightly. A change of masterbatch supplier, often made quietly to save cost, can change the shade more visibly. Black is especially sensitive: a different carbon black gives a warmer or cooler black, and under shop lights a box can look brownish or bluish next to the previous batch.
Let-down ratio
If the dosing unit drifts, or if the ratio is cut to save masterbatch, the color lightens and translucent parts become more see-through. White parts lose opacity and can look grey or yellowish.
Base resin and recycled content
Natural resin is not perfectly colorless. A change of resin lot or grade can shift the base tone, and recycled content usually adds a slight grey or yellow cast that pale colors show clearly. Regrind, trimmed or rejected parts ground and fed back into the mix, adds the same effect if the proportion changes. The recycled content note covers rPET and PCR PP.
Processing heat
Higher melt temperature or longer time in the barrel can yellow some pigments and resins slightly. Different machines, mold temperatures or cycle times can change gloss and therefore how a color reads, even when the pigment is identical.
Lids and bases from different processes
A storage bin injection molded in one plant and a lid made in another rarely match exactly, even with the same color reference. The same applies when a base is thermoformed and the lid is injection molded. Matching across processes needs a shared physical color standard and a check of both parts side by side.
Wall thickness
Translucent and tinted parts read darker where the wall is thicker. A thermoformed box that is thin in the corners and thicker in the base shows that as uneven color within one part. A batch run on slightly heavier sheet looks deeper in shade than the last one, even with the same masterbatch. Checking gram weight against the golden sample is therefore part of any color investigation on tinted parts.
Food contact and colorants
For food containers, the masterbatch is part of the food contact material. Its pigments and carrier must be suitable for food contact in the target market, for example under FDA 21 CFR 174-178 in the US or EU 10/2011 in the EU, and it should be named in the supplier declaration. A change of masterbatch on a food container is therefore not only a color question: the declaration and, where done, the migration test report should still cover the new material. The desk asks plants to notify any change of masterbatch or resin grade on food contact items before production, not after. See the food contact compliance guide and the additives and colorants note.
Diagnosis table
| Symptom | Likely cause | Check | Fix |
|---|---|---|---|
| Black looks brown or blue next to last batch | Different carbon black or masterbatch supplier | Compare with retained color standard | Fix masterbatch grade and supplier in order |
| Color lighter, parts more see-through | Lower let-down ratio | Ask for dosing record | Ratio stated and checked per batch |
| Pale colors look grey or yellow | Recycled content or regrind change | Ask for regrind policy and resin lot | Limit or fix regrind share |
| Slight yellowing on white parts | Higher melt heat or long residence | Compare parts from different machines | Plant adjusts process settings |
| Lids do not match bins | Different plants or processes | Check lid and base side by side | Shared physical standard, paired approval |
| Same color, different look | Gloss or texture difference | View under the same light | Specify finish as well as color |
Locking color down in the order
- Approve a physical color standard: a molded part or plaque in the real material, not a printed swatch or a screen color.
- Keep sets of the standard at the plant, with the desk and with the buyer.
- Name the masterbatch grade, let-down ratio and base resin in the order, and ask for notice of any change.
- State a regrind policy and any recycled content share.
- Define how color is judged: under which light, at what distance and against which tolerance, agreed per order.
- Compare first production parts with the standard before the full run, and again at pre-shipment inspection.
Where the plant has a color measuring instrument, readings can support the visual check; tolerances are agreed per order. The quality control page shows where color checks sit in the program.
Custom colors and minimums
Custom colors usually need a dedicated masterbatch run and a clean-out of the machine before and after, so they carry higher starting quantities than standard colors. Storage and organizer lines typically start at 1,000-3,000 pieces per item depending on size and mold; custom colors may need more, and the quantity is confirmed in writing per program. Reorders keep color more consistently when they are placed with the same plant and the same masterbatch, which is another reason to plan reorders early. See MOQ and lead time, and the OEM and private label page for brand color programs.
Next step
If a reorder has come in off-shade, keep parts from both batches and photograph them side by side under daylight. Send the photos, batch codes and the original standard through the quote form and the desk will trace the change with the plant.