Onyx Skin vs Earth Brown

How close are they?

ΔE 8.3, close: similar, with a visible difference side by side. Earth Brown is more saturated, warmer than Onyx Skin.

Can I use Earth Brown instead of Onyx Skin?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Earth Brown is more saturated, warmer than Onyx Skin.

Can I use Onyx Skin instead of Earth Brown?

The same difference applies the other way round: Onyx Skin is more muted, cooler.

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.