A brand's corporate navy shifting towards grey-purple in a new batch, a blouse bleeding onto a light background in its first wash, or a product hanging in the window fading from the sun within a few weeks — these all fall under a single heading: colour quality. Colour quality rests on two pillars. The first is colour fastness: the colour staying put against washing, rubbing, light and perspiration. The second is colour consistency: the same colour looking the same within a batch, between batches and on reorders. This article explains how the two are measured, what the ΔE (Delta E) number tells you, and what working to a ΔE<1 target on the dyeing line changes on the returns and waste side.
What colour fastness is, and its types
Colour fastness is a dyed fabric's ability to retain its colour against a particular agent. There is no single "fastness"; each agent has its own test and its own grade. A fabric can be wash-resistant yet fade quickly in light, or the other way around. That is why fastness is a specification chosen according to end use; the threshold expected of baby underwear is not the same as the threshold expected of an outerwear jacket.
| Fastness type | Which agent it measures | Practical significance |
|---|---|---|
| Wash fastness | Colour loss in washing and bleeding onto adjacent fabric (staining) | Critical in frequently washed underwear, babywear and casual wear; determines staining in mixed washes with light-coloured items. |
| Rubbing fastness | Colour transfer in dry and wet rubbing | Stands out in dark colours and indigo denim; indicates colour rubbing off onto skin, bags and light upholstery. |
| Light fastness | Fading under daylight/UV | Decisive for window-display items, curtains, outerwear and pieces exposed to light for long periods. |
| Perspiration fastness | Colour change against acidic and alkaline perspiration | In sportswear, underwear and summer collections; important at the underarm and collar areas that see a lot of sweat. |
Depending on end use, additional tests such as water fastness, chlorine/wash water, ironing and saliva (baby products) can be added to these four core headings. Fastness is largely determined by fibre–dye compatibility: on cotton, reactive dyeing forms a covalent bond with the fibre chain and so delivers high wash fastness; on polyester, disperse dyeing and the correct fixation step limit colour transfer caused by sublimation and migration.
How fastness is measured
Fastness is measured not by eye but with standard methods. The sample is exposed to the agent under controlled conditions (for example washed at a defined temperature and with a defined detergent, or held for a set time in a light cabinet), then the result is graded against two grey scales:
- Colour change (grey scale): How much the sample's own colour has changed is graded between 1 (changed a lot) and 5 (no change).
- Staining (bleeding): How much colour has transferred to the white multifibre strip washed together with the sample is again graded between 1 and 5.
- Light fastness: Compared against the blue wool reference scale and usually expressed as a grade between 1 and 8; a higher grade means slower fading.
These tests should be carried out in an accredited laboratory and under conditions that make the result objective. At KARCEM, fastness tests are a standard step of post-finishing quality control; results are reported on a batch basis. Colour assessment is also carried out in a light cabinet: the same fabric is examined under different light sources such as daylight, store lighting and store-type fluorescent. This is because two colours looking equal under one light but different under another (metamerism) is a common trap that can only be caught in a standard cabinet.
What ΔE is, and how it is measured
Talking about how different two colours are with subjective phrases like "a bit lighter" is no use in production. ΔE (Delta E) is a standard measure that reduces the difference between two colours to a single number. Colour is defined in CIELAB space by three axes: L* (lightness–darkness), a* (green–red) and b* (blue–yellow). ΔE is the resultant of the differences across these three axes between the target colour and the measured colour. Roughly: the smaller the ΔE, the closer the two colours are; zero means an exact match.
The measurement is made not by eye but with a spectrophotometer. The instrument measures the light reflected off the surface wavelength by wavelength and converts the colour into L*a*b* values. This turns colour from something dependent on the operator's eye, their tiredness or the day's lighting into data that can be recorded. The measurement of the target colour (standard) is compared with the measurement of the produced batch, and the ΔE between them is reported. The thresholds below summarise roughly what ΔE values correspond to in human perception.
| ΔE range | Perceptual equivalent | Meaning in production |
|---|---|---|
| 0 – 1 | Even a trained eye cannot tell them apart | Commercial "exact match"; a safe target on reorders. |
| 1 – 2 | A trained eye can tell them apart on close inspection | Acceptable in most applications; borderline for sensitive brands. |
| 2 – 3.5 | The difference is obvious when placed side by side | Noticeable on adjacent panels of the same product; usually needs revision. |
| 3.5 and above | Marked colour difference | Typically grounds for rejection; redyeing or correction is required. |
Note that the thresholds are given within a "typically" frame: the acceptance limit is defined in the contract according to the colour, fibre type, end use and the brand's tolerance. Because the eye is more sensitive to light and neutral tones, the same ΔE value can look more disturbing than it would on dark tones.
What ΔE<1 means in practice
A ΔE<1 target is not just a single measurement; it is a commitment that the colour stays consistent across three separate dimensions:
- Within-batch consistency: The start, middle and end of the rolls coming out of the same dyeing batch are the same colour. When the body and sleeve of a shirt are cut from different rolls, no colour difference arises.
- Between-batch consistency: Batches dyed on different days, in different vessels, sit on the same target. Two production batches of the same order are indistinguishable when hung side by side in the store.
- Reorder consistency: On a new order placed months later, the colour stays the same as the first production. A brand's unchanging corporate colour, or an ongoing collection, looks the same across seasons.
What makes this possible is not "hitting" the colour but recording it. Every approved colour is archived together with its recipe (dye type, concentration, process conditions) and its spectrophotometric measurement. On a reorder the same recipe is called up, applied with automatic dosing, and the result is again verified with the light cabinet and a ΔE measurement. Setting the target at ΔE<1 rather than "ΔE<0" is deliberate: zero difference cannot be physically guaranteed, but below 1 is a difference indistinguishable by eye in practice — that is, a realistic and measurable definition of the commercial "exact match".
Frequently asked questions
What is the difference between colour fastness and colour consistency?
They are two separate things. Colour fastness is the colour staying put against washing, rubbing, light and perspiration. Colour consistency, by contrast, is the same colour looking the same within a lot, between lots and on re-order. A lot can match the target shade exactly (low ΔE) yet, if its wash fastness is poor, the colour will shift on the first wash. Neither one alone guarantees quality; both must be specified together.
Which fastness types are tested and where are they critical?
There are four core categories: wash fastness (critical in frequently washed underwear, babywear and casualwear), rubbing fastness (prominent in dark shades and indigo/vat denim), light fastness (decisive for window-display goods, curtains and outerwear) and perspiration fastness (in sportswear, underwear and summer collections). Depending on end use, additional tests can be added, such as fastness to water, to chlorinated/wash water, to ironing and to saliva for babywear.
Which scales are used to grade fastness tests?
Fastness is measured not by eye but by standard methods, and graded on two grey scales. Colour change is rated from 1 (severe change) to 5 (no change), and staining (bleed) likewise from 1 to 5, graded on the colour transferred to a white multifibre strip. Light fastness, on the other hand, is compared against the blue wool reference scale and generally expressed from 1 to 8; a higher rating means slower fading. Tests must be carried out in an accredited laboratory.
What is ΔE (Delta E) and how is it measured?
ΔE is a standard measure that reduces the difference between two colours to a single number. Colour is defined in CIELAB space by three axes: L* (lightness-darkness), a* (green-red) and b* (blue-yellow). ΔE is the resultant of the difference across these three axes; the smaller it is, the closer the colours, with zero being a perfect match. Measurement is done not by eye but with a spectrophotometer; the instrument measures reflected light wavelength by wavelength and converts the colour into data that can be archived.
What do ΔE values mean in terms of acceptance?
In the 0-1 range even a trained eye cannot tell them apart; a commercial perfect match and a safe target for re-orders. 1-2 is discernible on close inspection, acceptable in most applications, borderline for exacting brands. 2-3.5 is clearly different when placed side by side and generally requires revision. 3.5 and above is a distinct colour difference, typically grounds for rejection. The acceptance limit is defined in the contract according to the colour, fibre type, end use and the brand's tolerance.
What does a ΔE<1 target commit to in practice?
ΔE<1 is not a single measurement but the colour staying consistent in three dimensions: within a lot (the start, middle and end of rolls from the same lot are identical), between lots (lots dyed on different days and in different vessels land on the same target) and consistency on re-order. What makes this possible is recording the colour; the recipe and spectrophotometric measurement are archived, and on re-order the same recipe is called up. The target is ΔE<1 because zero difference cannot be physically guaranteed.
Impact on the brand: returns and waste
Colour consistency is not an aesthetic detail but a direct cost item. When the colour target is missed, the consequences accumulate in three places. Before production: when the ΔE threshold is exceeded the batch is rejected, redyed or scrapped; this means water, chemicals, energy and time spent a second time in the contract manufacturing process. After dispatch: a colour difference between batches of the same model, or between the product photo and the delivered product in e-commerce, raises the rate of returns and exchanges; the cost of return logistics and restocking can be greater than the product itself. On the brand side: a corporate colour that does not settle or that fades directly erodes perceived quality and repeat purchase.
Working to a ΔE<1 target and with standard fastness tests shrinks all three of these items from the outset. When colour is approved and recorded before production, surprise batches and the rework tied to them decrease; when fastness thresholds are correctly chosen according to end use, complaints after washing and use drop. The practical summary: a measured and reported colour is always cheaper than a guessed colour.
To see the steps of the dyeing and printing process beyond colour (pre-treatment, reactive/disperse selection, printing techniques and finishing) together, you can look at the dyeing and printing guide, and for technical terms encountered for the first time you can refer to the Glossary.
With KARCEM
KARCEM knits greige on its own machines and coordinates dyeing, printing and finishing through a vetted contract network; this means colour is coordinated under a single point of contact, from its recipe to the finished fabric. We run colour matching with spectrophotometric measurement and a light cabinet, verify within-batch and between-batch consistency to a ΔE<1 target on the incoming lot, and confirm wash, rubbing, light and perspiration fastness with accredited tests. Because every colour is recorded in the sample → approval → production flow, your colour stays the same on reorders. To clarify your colour and fastness specification, send us your sample and quote request; let our team guide you so you start with the right tolerance.