Onyx Skin vs Volcano Brown

How close are they?

ΔE 8.2, close: similar, with a visible difference side by side. Volcano Brown is a little darker, cooler than Onyx Skin.

Can I use Volcano Brown instead of Onyx Skin?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Volcano Brown is a little darker, cooler than Onyx Skin.

Can I use Onyx Skin instead of Volcano Brown?

The same difference applies the other way round: Onyx Skin is a little lighter, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.