Shadow Thorn vs Dark Grey Blue

How close are they?

ΔE 8.7, close: similar, with a visible difference side by side. Dark Grey Blue is more muted, warmer than Shadow Thorn.

Can I use Dark Grey Blue instead of Shadow Thorn?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Dark Grey Blue is more muted, warmer than Shadow Thorn.

Can I use Shadow Thorn instead of Dark Grey Blue?

The same difference applies the other way round: Shadow Thorn is 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.