ΔE 14.3, fair: the same colour family, but not a straight swap. Night Lords Blue is a little darker, cooler than Necromancer Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Night Lords Blue is a little darker, cooler than Necromancer Purple.
The same difference applies the other way round: Necromancer Purple is a little lighter, 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 Necromancer Purple on the colour wheel See Night Lords Blue on the colour wheel
All matches: Necromancer Purple equivalents · Night Lords Blue equivalents