How close is close? Reading ΔE in Model Box
Paweł Krystkiewicz
Every color match in Model Box carries a ΔE score, shown as a number and a traffic-light dot.
0.8, 2.4, 7.1.
The number puts a figure on the difference between two colors. It decides whether a paint makes the substitutes list at all, how the list is ordered, and where your tolerance cuts it off. The highest value you can set is 15. Anything higher makes no sense, and we explain why in this article.
What goes into ΔE
Take two colors. Place them in the three-dimensional OKLab space, measure the straight-line distance between the two points, multiply by 100. That is how we compute the ΔE we show in Model Box. OKLab is a color space built so that equal distances look like equal differences to a person, whatever the hue and whatever the lightness. The ×100 only moves the decimal point: distances land between 0 and 100 instead of between 0.00 and 1.00. Two paints rarely sit more than 20 apart; pure black against pure white is the full 100.
It is not the ΔE76 or ΔE2000 used in print and textile work. Those are computed in CIELAB, a different scale, so their numbers do not carry over. A tolerance of 2 quoted for print refers to a different ruler. It is not a percentage either: 10.0 does not mean 10% off. It means five times the smallest difference a standard observer picks up.
What it means to the eye
On this scale the just-noticeable difference is ΔE = 2, the figure the CSS Color Level 4 specification gives for OKLab, and the point where two chips compared side by side read as noticeably different colors. The bigger the number, the more obvious the difference. Above 10 the two colors have nothing to do with each other. The scale below shows how we in Model Box read the distance against the human eye, and with it how useful a substitute paint will be.
- Identical matchIndistinguishable. Use as a direct substitute.≤ 1
- Excellent matchSubtle difference when compared side-by-side.≤ 2
- Close matchVisibly different. Often a similar shade.≤ 3.5
- Same color familyClearly different. Works for general use or mixing.≤ 6
- Similar colorNoticeably different. Best as a mixing base.≤ 10
- Distant colorDifferent color. Significant adjustment needed.≤ 15
- Different colorNot a substitute.> 15
One caveat. ΔE is only the absolute distance between two colors in the space. It says nothing about direction: which way the hue drifted. So several candidates for, say, a grey can sit at the same ΔE and still lean blue, pink or green. The final call on a substitute is yours.
The scale, applied
The pairs below walk through each band of the scale: a direct side-by-side comparison and the ΔE that falls out of it. The color values are the ones the manufacturers publish in their catalogues.
Most likely the same pigment, whatever the solvent. GSI prints the same artwork for Mr. Color, Aqueous, Acrysion and the spray can.
Same maker, same name, two ranges - and Vallejo itself lists one as the other’s equivalent. The published values still differ: a different pigment, or a slip in the catalogue.
A real-life cross-brand match. Similar chemistry, same solvent; similar colors, but a slightly different shade once you put them side by side.
Clearly different shades.
A different brown. You can see it from across the bench. A base to lighten, at best.
Different colors altogether.
Both sold as Dunkelgelb, one with the RAL number on the label. On paper, unrelated colors.
Setting the tolerance
The Tolerance ΔE field in Settings is the cutoff for the substitutes list. Lower ΔE means fewer results, closer to the original. Higher ΔE means more results that need more work from you. The color scale next to the field shows how tight your matches will be. We set it to 3 by default.
- up to 2, when you want to stay close to the colors called out in the instructions.
- up to 3.5, when nothing good turns up among the paints you own or the brands you picked.
- up to 6, when you want a base to modulate or mix from.
- Above 10 the list stops meaning much. Most paints in a similar color but a clearly different shade qualify.
What ΔE does not tell you
We compute ΔE from two stored values, and the stored values come from manufacturers’ catalogues, not from a colorimeter reading of the paint. Everything that happens outside the catalogue moves the result: thinning, primer, batch, the lamp over your bench, gloss. Metallics and pearls are hard to compare at all; they will “match” most light greys. Check the substitute you picked on plastic before you paint the whole model.
A ΔE of 2 is where the eye starts seeing a difference, and 6 is where mixing starts. Every match we show in the app sits somewhere between those two points, and the tolerance setting decides how far along that scale you are willing to go.