A buyer's merchandiser at Northline Apparel signs off a colour approval every time a bulk order moves toward dyeing. Two problems can hide inside a colour approval that looks perfectly fine at first glance. The first is shade variation: a small, normal difference in colour between separate dye lots, even when both were dyed to the same colour standard. The second is metamerism: two colours that match under one light source but look different under another. A merchandiser who does not know the difference between these two problems, or who checks a colour under only one light source, risks approving a colour that later mismatches on the shop floor.
This lesson mainly teaches a decision: is a colour approval complete, or does it need a second check. Without this skill, a merchandiser at Northline Apparel could approve Order A's fabric colour after seeing it once, under one light, and only discover a mismatch once the T-shirts are already in a shop window lit differently from the room where the approval was signed.
You need: the idea of a colour standard and a lab dip from lessons 3.4.1 and 3.4.2. If you have not read those lessons, the key terms below give you enough to continue.
By the end of this lesson you can:
Not covered here: how a colour standard is first set (lesson 3.4.1), how lab dips and strike-offs are approved (lesson 3.4.2), and how to read a full colour approval report (lesson 3.4.3).
| Term | Meaning |
|---|---|
| Dye lot | One batch of fabric dyed together in the same vat, which can differ slightly in shade from another batch of the same colour. |
| Shade match | Visual or instrument comparison of a fabric's colour against an approved swatch. |
| Shade band | A visible band of colour variation across a fabric roll from uneven dyeing. |
| Colour fastness | A rating for how well a fabric's dye resists fading or bleeding, usually stated as a numeric grade in a report's colour fastness section. |
| Shade variation | A difference in colour between separate dye lots or rolls, even when both were dyed to the same colour standard. |
| Metamerism | When two colours that match under one light source look different under another light source. |
Shade variation is a difference in colour between separate dye lots or rolls, even when both were dyed to the same colour standard — a normal, small variation that quality tolerances allow for, not a fault by itself. A tolerance range states how much of this normal variation is acceptable before a lot is treated as a genuine mismatch, so shade variation is managed by comparing a measured gap against that agreed range, not by expecting a perfect, zero-variation result from every dye lot a mill runs.
Metamerism is a different problem entirely: it is when two colours that match under one light source, such as daylight, look different under another, such as indoor fluorescent light. The two dyed samples can be chemically different from one another even though they appear identical under one particular light, because different dye combinations can reflect light in slightly different ways that only become visible once the light itself changes. Metamerism is therefore a real risk whenever a colour approval was checked under only one light source, no matter how carefully that single check was carried out. Both issues are reasons a genuine colour approval should specify tolerances for shade variation and check under more than one lighting condition for metamerism, rather than assuming that a single check, under a single light, is sufficient for either problem.
| What can differ | The shapes you meet | Why it matters |
|---|---|---|
| Shade variation between dye lots | A normal, expected small difference between separate lots dyed to the same colour standard; quality tolerances allow for it rather than requiring a perfect, zero-variation match. | Rejecting every small lot-to-lot difference as a fault would reject fabric that is genuinely within tolerance, wasting good fabric. |
| Metamerism | Two colours matching under one light source but differing under another; a garment approved only under daylight might visibly mismatch its trims or a customer's own reference sample under store lighting. | A colour that passes one light-source check can still fail in the real place the garment is seen, if that check was never done under a second light source. |
| Checking under multiple light sources | The standard practice to catch metamerism before bulk approval: checking a colour standard and its match under at least two different light types, for example daylight and a standard indoor light. | This is the one check that specifically catches metamerism; a shade-variation check between lots does not catch it on its own. |
| Confusing the two | Treating a lot-to-lot difference as if it were a lighting problem, or treating a lighting difference as if it were a bad dye lot. | Misdiagnosing the issue leads to the wrong fix: rejecting a good dye lot, or approving a fabric that will still mismatch under a different light. |
Northline Apparel's buyer needs to confirm that Order A's own colour approval was checked under more than one light source before finalising the approval. Order A's T-shirts will be seen under daylight, through the shop's own front windows, and under indoor lighting, on the shop floor further inside. This is an export order made to order for Northline Apparel, so the buyer's own team, not just Delta Garments' quality team, carries responsibility for confirming the approval is genuinely complete before bulk dyeing begins.
Delta Garments' quality team submitted the approval after checking the dyed fabric against Order A's colour standard, and the result looked like a clean match. But a clean match seen once, under one light, is not the same claim as a clean match confirmed under every light the finished T-shirts will actually meet. Because Order A ships to Northline Apparel's own shops rather than to a domestic customer seen only under one shop's fixed lighting, the buyer treats the daylight-and-indoor-light check as a standard step, not an optional extra, before bulk dyeing goes ahead on the full 15,000-piece order.
The worked numberOrder A's colour approval does not need a new money figure to make its point. The worked output of this lesson is correctly identifying that a colour approval checked under only one light source is incomplete, and that shade variation and metamerism are two distinct issues requiring two distinct responses: a shade-variation gap is checked against a tolerance range; a metamerism risk is checked by adding a second light source, not by re-measuring the same sample under the same light again.
A common mistake is assuming that a colour matching perfectly under one light source is fully approved. A colour standard and its match should be checked under more than one lighting condition, since a genuine metamerism issue would not show up under a single check. A merchandiser who signs off an approval seen only in the mill's own daylight-lit lab, without checking it under a standard indoor light as well, has not actually ruled out metamerism — the fabric could still mismatch its trims or a customer's reference sample the moment it reaches a shop lit differently.
Two dye lots of the same colour standard can look very slightly different from each other; this is shade variation, and a small amount of it is normal and allowed. A separate problem is when one single colour looks fine under one kind of light, such as daylight, but looks different under another kind of light, such as indoor lighting; this is called metamerism. A colour check done under only one light cannot catch metamerism, because the problem only shows up when the light changes. Before finalising any colour approval, check whether it was tested under more than one light source. If it was only tested under one, ask for a second check under a different light before treating the colour as approved.
The document the buyer reads, the approval note exactly as summarised:
You are the buyer's merchandiser at Northline Apparel. Is this approval complete? Decide before you open the decision.
Not yet. The buyer should request a second check under indoor lighting, or another relevant light source, before finalising the approval.
First, the approval note names only one light source. Daylight is one of the two conditions the T-shirts will actually be seen under; the note says nothing about indoor lighting, the other condition.
Second, a colour that matches under daylight alone could still exhibit metamerism under a different lighting condition. Metamerism does not show up in a daylight-only check by definition, because it is specifically a difference that appears when the light source changes. Approving now, on this note alone, would leave that risk completely unchecked.
If the second check under indoor lighting also shows a match, the approval can be finalised with confidence covering both conditions the garment will be seen in. If it shows a mismatch instead, the mill needs to adjust the dye formulation before bulk dyeing begins, not after.
Framed qualitatively, since this is not a fixed money figure for Order A: approving a colour under only one light source risks a garment that visibly mismatches its trims, or mismatches a customer's own expectation, once it is actually seen under a different light in the shop. That mismatch can mean a rejected shipment at the buyer's own quality inspection, a markdown once the mismatch is spotted in-store, or a returned garment from a customer who compared it under different lighting to something else in the same outfit. None of these outcomes is separately quantified in Order A's own fixed figures, but every one of them is a real cost this lesson's multi-light-source check is designed to prevent, for the small extra time of a second check before bulk dyeing.
Open the colour approval tracker linked at the top of this lesson. Its Tracker sheet already carries each approval stage's submitted and decided dates and its status. Use the same sheet to note, against each stage, whether more than one light source was checked before that stage moved to "Approved."
| Question | Order A (filled in) | Your order |
|---|---|---|
| Colour standard reference | CS-4471 | |
| Light sources named in the approval note | Daylight only | |
| Is a second light source needed? | Yes — indoor light not yet checked | |
| Second check requested? | Yes, before finalising |
1. What is shade variation?
2. What is metamerism?
3. A mill's approval note for a 500-piece domestic reorder at Cedar & Co. states: 'Checked against standard under indoor fluorescent light only. Result: match.' Is this approval complete?
| EN | AR | FR | TR | Meaning |
|---|---|---|---|---|
| Dye lot | دفعة الصباغة | Lot de teinture | Boya partisi | One batch of fabric dyed together in the same vat, which can differ slightly in shade from another batch of the same colour. |
| Shade match | تطابق درجة اللون | Correspondance de nuance | Renk (ton) eşleşmesi | Visual or instrument comparison of a fabric's colour against an approved swatch. |
| Shade band | شريط تفاوت اللون | Bande de nuance | Ton bandı | A visible band of colour variation across a fabric roll from uneven dyeing. |
| Colour fastness | ثبات اللون | Solidité des couleurs | Renk haslığı | A rating for how well a fabric's dye resists fading or bleeding, usually stated as a numeric grade in a report's colour fastness section. |
| Shade variation | تفاوت درجة اللون | Variation de nuance | Ton farkı | A difference in colour between separate dye lots or rolls, even when both were dyed to the same colour standard. |
| Metamerism | الميتاميريزم | Métamérisme | Metamerizm | When two colours that match under one light source look different under another light source. |
You now know how to check whether a colour approval covered more than one light source. The next lesson brings this course's four lessons together into one tracked approval sequence, using the colour approval tracker on a full bulk order. Back to the course map