Cobalt Blue vs Blue Violet

How close are they?

ΔE 22.8, loose: different enough that you should pick on purpose. Blue Violet is a little lighter, much more muted than Cobalt Blue.

Can I use Blue Violet instead of Cobalt Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Blue Violet is a little lighter, much more muted than Cobalt Blue.

Can I use Cobalt Blue instead of Blue Violet?

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