Black Forest vs Unforgiven Green

How close are they?

ΔE 8.2, close: similar, with a visible difference side by side. Unforgiven Green is a little darker, more muted than Black Forest.

Can I use Unforgiven Green instead of Black Forest?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Unforgiven Green is a little darker, more muted than Black Forest.

Can I use Black Forest instead of Unforgiven Green?

The same difference applies the other way round: Black Forest 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.