ΔE 14.9, fair: the same colour family, but not a straight swap. Imperial Purple is noticeably lighter, more muted than Naggaroth Night.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Imperial Purple is noticeably lighter, more muted than Naggaroth Night.
The same difference applies the other way round: Naggaroth Night is noticeably darker, 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.
See Naggaroth Night on the colour wheel See Imperial Purple on the colour wheel
All matches: Naggaroth Night equivalents · Imperial Purple equivalents