ΔE 11.5, fair: the same colour family, but not a straight swap. Omega Blue is more muted, cooler than Nightshade Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Omega Blue is more muted, cooler than Nightshade Purple.
The same difference applies the other way round: Nightshade Purple is 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 Nightshade Purple on the colour wheel See Omega Blue on the colour wheel
All matches: Nightshade Purple equivalents · Omega Blue equivalents