Russian Blue Base vs Corvus Black

How close are they?

ΔE 8.6, close: similar, with a visible difference side by side. Corvus Black is a little lighter, more muted than Russian Blue Base.

Can I use Corvus Black instead of Russian Blue Base?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Corvus Black is a little lighter, more muted than Russian Blue Base.

Can I use Russian Blue Base instead of Corvus Black?

The same difference applies the other way round: Russian Blue Base is a little darker, 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.