Atramentum Black vs Flesh Wash

How close are they?

ΔE 36.4, loose: different enough that you should pick on purpose. Flesh Wash is noticeably lighter, much more saturated than Atramentum Black.

Can I use Flesh Wash instead of Atramentum Black?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 36). Flesh Wash is noticeably lighter, much more saturated than Atramentum Black.

Can I use Atramentum Black instead of Flesh Wash?

The same difference applies the other way round: Atramentum Black is noticeably darker, much more muted.

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.