ΔE 14.8, fair: the same colour family, but not a straight swap. Naggaroth Night is a little darker, more muted, cooler than Diabolic Plum.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Naggaroth Night is a little darker, more muted, cooler than Diabolic Plum.
The same difference applies the other way round: Diabolic Plum 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 Diabolic Plum on the colour wheel See Naggaroth Night on the colour wheel
All matches: Diabolic Plum equivalents · Naggaroth Night equivalents