Grimoire Purple vs Purple Black

How close are they?

ΔE 17.2, loose: different enough that you should pick on purpose. Purple Black is a little darker, much more muted than Grimoire Purple.

Can I use Purple Black instead of Grimoire Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Purple Black is a little darker, much more muted than Grimoire Purple.

Can I use Grimoire Purple instead of Purple Black?

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