Unforgiven Green vs Mars Black

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Mars Black is a little darker, more muted than Unforgiven Green.

Can I use Mars Black instead of Unforgiven Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Mars Black is a little darker, more muted than Unforgiven Green.

Can I use Unforgiven Green instead of Mars Black?

The same difference applies the other way round: Unforgiven Green is a little lighter, 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.