Onyx Skin vs Battle of Marathon

How close are they?

ΔE 6.9, close: similar, with a visible difference side by side. Battle of Marathon is a little lighter, warmer than Onyx Skin.

Can I use Battle of Marathon instead of Onyx Skin?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Battle of Marathon is a little lighter, warmer than Onyx Skin.

Can I use Onyx Skin instead of Battle of Marathon?

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