Dark Green vs Flat Green

How close are they?

ΔE 9.8, close: similar, with a visible difference side by side. Flat Green is a little lighter, more muted, warmer than Dark Green.

Can I use Flat Green instead of Dark Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Flat Green is a little lighter, more muted, warmer than Dark Green.

Can I use Dark Green instead of Flat Green?

The same difference applies the other way round: Dark Green is a little darker, more saturated, cooler.

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.