ΔE 16.7, loose: different enough that you should pick on purpose. Imperial Purple is more saturated, warmer than Alien Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Imperial Purple is more saturated, warmer than Alien Purple.
The same difference applies the other way round: Alien Purple is 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 Alien Purple on the colour wheel See Imperial Purple on the colour wheel
All matches: Alien Purple equivalents · Imperial Purple equivalents