Deep Violet vs Grimoire Purple

How close are they?

ΔE 17.2, loose: different enough that you should pick on purpose. Grimoire Purple is a little lighter, more muted, warmer than Deep Violet.

Can I use Grimoire Purple instead of Deep Violet?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Grimoire Purple is a little lighter, more muted, warmer than Deep Violet.

Can I use Deep Violet instead of Grimoire Purple?

The same difference applies the other way round: Deep Violet is a little 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.