ΔE 52.4, loose: different enough that you should pick on purpose. Atramentum Black is noticeably darker, much more muted than Kroak Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 52). Atramentum Black is noticeably darker, much more muted than Kroak Green.
The same difference applies the other way round: Kroak Green is noticeably lighter, much more saturated.
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.
See Kroak Green on the colour wheel See Atramentum Black on the colour wheel
All matches: Kroak Green equivalents · Atramentum Black equivalents