Malignant Green vs Orc Skin

How close are they?

ΔE 55.8, loose: different enough that you should pick on purpose. Orc Skin is noticeably darker, much more muted, cooler than Malignant Green.

Can I use Orc Skin instead of Malignant Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 56). Orc Skin is noticeably darker, much more muted, cooler than Malignant Green.

Can I use Malignant Green instead of Orc Skin?

The same difference applies the other way round: Malignant Green is noticeably lighter, much more saturated, warmer.

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.