ΔE 8.3, close: similar, with a visible difference side by side. Crimson Hell is a little darker, more muted, cooler than Grimoire Purple.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Crimson Hell is a little darker, more muted, cooler than Grimoire Purple.
The same difference applies the other way round: Grimoire Purple is a little lighter, more saturated, warmer.
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.
See Grimoire Purple on the colour wheel See Crimson Hell on the colour wheel
All matches: Grimoire Purple equivalents · Crimson Hell equivalents