Ash Black vs Ink Black Green

How close are they?

ΔE 29.2, loose: different enough that you should pick on purpose. Ink Black Green is noticeably darker, more saturated than Ash Black.

Can I use Ink Black Green instead of Ash Black?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Ink Black Green is noticeably darker, more saturated than Ash Black.

Can I use Ash Black instead of Ink Black Green?

The same difference applies the other way round: Ash Black is noticeably lighter, 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.