Prussian Blue vs Blue Violet

How close are they?

ΔE 16.6, loose: different enough that you should pick on purpose. Blue Violet is noticeably lighter, more muted, warmer than Prussian Blue.

Can I use Blue Violet instead of Prussian Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Blue Violet is noticeably lighter, more muted, warmer than Prussian Blue.

Can I use Prussian Blue instead of Blue Violet?

The same difference applies the other way round: Prussian Blue is noticeably darker, 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.