ΔE 17.5, loose: different enough that you should pick on purpose. Alien Purple is a little lighter, warmer than Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Alien Purple is a little lighter, warmer than Blue.
The same difference applies the other way round: Blue is a little darker, 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 Blue on the colour wheel See Alien Purple on the colour wheel
All matches: Blue equivalents · Alien Purple equivalents