Short answer
Never let colour be the only way information is carried, and make text contrast with its background in lightness, not just hue. Red–green colour codes such as nutrition traffic lights and variant colours lose much of their separation under common colour vision deficiencies, and small, low-contrast text on shiny or coloured substrates is the most common legibility failure on packs.
Colour vision deficiency is common: the US National Eye Institute describes red–green forms as by far the most frequent, affecting many more men than women. Low vision and age-related changes add to this — the lens yellows and scatters more light with age, reducing contrast and making blues and dark colours harder to separate. A pack is read quickly, at arm's length, often in poor light, by people of every age. Designing for colour vision deficiency and for reduced contrast sensitivity helps everyone under those conditions, not only people with a diagnosis.
The UK front-of-pack nutrition scheme combines red, amber and green colour coding with percentage reference intakes; its guidance says the words 'High', 'Medium' and 'Low' may additionally be used to reinforce the colours. The table shows why that option matters. With typical colour vision the three colours are far apart. Under a simulation of deuteranopia, red and green fall to under 10 units apart on the CIEDE2000 scale, under protanopia amber and green do the same, and in greyscale red and green are also close, because they have similar lightness. The same applies to variant codes: a red 'full-fat' and green 'reduced' pack of similar lightness may look alike to a large number of shoppers. Research supports the value of the colour itself — a multi-country study found traffic-light labels helped people pick the healthier product better than black-and-white ones — so the fix is redundancy, not removing colour.
EU food-information law, retained in UK law, defines legibility to include type colour, the surface of the material and 'significant contrast between the print and the background', and sets a minimum x-height of 1.2 mm for mandatory particulars (0.9 mm on packs whose largest surface is under 80 cm²). It does not give a numeric contrast ratio. The web's WCAG ratios were written for screens, but the underlying idea — contrast of luminance, not hue — transfers: dark text on a light ground, or the reverse, survives glare, dim light and colour vision deficiency; red text on green, or mid-grey on silver, does not. Metallic and clear films are the hardest: their apparent lightness changes with angle, so text that reads in one position vanishes in another unless it sits on an opaque white or dark panel.
WCAG 2.2 contrast thresholds apply to web content. They are a useful benchmark for print, not a requirement for packaging.
Separate coded colours in lightness as well as hue, so that the code survives greyscale. Pair every colour code with a word, number, symbol or position — 'High' beside red, a distinct icon beside each variant. Put mandatory text on a solid, matt panel rather than directly on foil, film or busy imagery. Check designs through colour-vision simulations and a greyscale conversion before proofing, and then check the printed proof in dim, warm light, because on-screen checks cannot show glare, metallic flip or ink density.
| Viewing condition | Red vs amber | Red vs green | Amber vs green |
|---|---|---|---|
| Typical colour vision | 37.5 | 71.0 | 40.7 |
| Protanopia (simulated) | 33.8 | 27.4 | 7.7 |
| Deuteranopia (simulated) | 18.4 | 7.9 | 17.1 |
| Greyscale (lightness only) | 21.3 | 10.9 | 10.6 |
| Background | Black text | White text |
|---|---|---|
| Red (#e6281e) | 4.7:1 | 4.5:1 |
| Amber (#f5aa1e) | 10.7:1 | 2.0:1 |
| Green (#3caa46) | 7.0:1 | 3.0:1 |
Why: Variants are distinguished by red and green of similar lightness, which merge under red–green colour vision deficiency.
Fix: Change one colour's lightness substantially and add the variant name or an icon in a consistent position.
Why: Metallic film changes apparent lightness with angle, so text contrast collapses in some positions.
Fix: Print mandatory text on an opaque white or dark matt panel.
Why: Ink on the substrate is lighter or duller than the screen colour, and glare from film or varnish lowers contrast further.
Fix: Check contrast on a printed proof under dim and glare conditions; move to black or white text where it is marginal.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
StandardStrong evidence
The UK front-of-pack nutrition label scheme combines red, amber and green colour coding with percentage reference intakes, and its guidance allows 'High', 'Medium' and 'Low' text to be added to reinforce the meaning of the colours.
Caveat: Voluntary UK guidance, last updated in 2016; not compliance advice.
StandardStrong evidence
EU Regulation 1169/2011 defines legibility to include type colour, the surface of the material and significant contrast between print and background, and requires mandatory particulars to have an x-height of at least 1.2 mm, or 0.9 mm where the pack's largest surface is under 80 cm².
Caveat: Read in the UK-retained version; provisions may differ by jurisdiction after amendment. Not legal advice.
Colourwise analysisModerate evidence
Under a Viénot–Brettel–Mollon simulation of deuteranopia, typical printed red and green traffic-light colours fall to under 10 CIEDE2000 units apart, compared with about 70 units for typical colour vision.
Based on: Calculated by Colourwise with src/lib/colour/cvd.ts and CIEDE2000 on illustrative sRGB stand-ins for the three colours; see the table on this page.
Caveat: Illustrative colours, not official values; simulations model complete dichromacy, and printed colours vary with ink and substrate.
Source: Digital video colourmaps for checking the legibility of displays by dichromats; Guide to creating a front of pack (FoP) nutrition label for pre-packed products sold through retail outlets
FactModerate evidence
In a multi-country study included in a systematic review, traffic-light-coloured nutrition labels helped participants identify the healthier product better than black-and-white labels.
Caveat: Reported in a review; a choice task, not a purchase study.
FactStrong evidence
Red–green colour vision deficiency is the most common form and affects men far more often than women.
Source: Colour Blindness / Colour Vision Deficiency (patient guidance)
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.