ΔE 20.9, loose: different enough that you should pick on purpose. Alien Purple is a little darker, much more saturated, warmer than Faded Ultramarine.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Alien Purple is a little darker, much more saturated, warmer than Faded Ultramarine.
The same difference applies the other way round: Faded Ultramarine is a little lighter, 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 Faded Ultramarine on the colour wheel See Alien Purple on the colour wheel
All matches: Faded Ultramarine equivalents · Alien Purple equivalents