ΔE 20.3, loose: different enough that you should pick on purpose. Alien Purple is much more saturated, warmer than Medium Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Alien Purple is much more saturated, warmer than Medium Blue.
The same difference applies the other way round: Medium Blue is much 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 Medium Blue on the colour wheel See Alien Purple on the colour wheel
All matches: Medium Blue equivalents · Alien Purple equivalents