Necromancer Purple vs Calgar Blue

How close are they?

ΔE 21.0, loose: different enough that you should pick on purpose. Calgar Blue is a little lighter, more saturated, cooler than Necromancer Purple.

Can I use Calgar Blue instead of Necromancer Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Calgar Blue is a little lighter, more saturated, cooler than Necromancer Purple.

Can I use Necromancer Purple instead of Calgar Blue?

The same difference applies the other way round: Necromancer Purple is a little darker, more muted, 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.