ΔE 12.9, fair: the same colour family, but not a straight swap. Blue is a little darker, cooler than Imperial Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Blue is a little darker, cooler than Imperial Purple.
The same difference applies the other way round: Imperial 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 Imperial Purple on the colour wheel See Blue on the colour wheel
All matches: Imperial Purple equivalents · Blue equivalents