Drake Tooth vs Gray Green

How close are they?

ΔE 7.7, close: similar, with a visible difference side by side. Gray Green is a little darker, cooler than Drake Tooth.

Can I use Gray Green instead of Drake Tooth?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Gray Green is a little darker, cooler than Drake Tooth.

Can I use Drake Tooth instead of Gray Green?

The same difference applies the other way round: Drake Tooth is a little lighter, 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.