Dark Blue vs Violet Vamp

How close are they?

ΔE 7.5, close: similar, with a visible difference side by side. Violet Vamp is a little lighter, warmer than Dark Blue.

Can I use Violet Vamp instead of Dark Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Violet Vamp is a little lighter, warmer than Dark Blue.

Can I use Dark Blue instead of Violet Vamp?

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