Blue vs Violet Vamp

How close are they?

ΔE 16.3, loose: different enough that you should pick on purpose. Violet Vamp is a little darker, warmer than Blue.

Can I use Violet Vamp instead of Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Violet Vamp is a little darker, warmer than Blue.

Can I use Blue instead of Violet Vamp?

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