ΔE 12.5, fair: the same colour family, but not a straight swap. Imperial Purple is a little lighter, more saturated, warmer than Royal Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Imperial Purple is a little lighter, more saturated, warmer than Royal Purple.
The same difference applies the other way round: Royal Purple is a little darker, more muted, cooler.
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 Royal Purple on the colour wheel See Imperial Purple on the colour wheel
All matches: Royal Purple equivalents · Imperial Purple equivalents