Ultramarine vs Alien Purple

How close are they?

ΔE 17.5, loose: different enough that you should pick on purpose. Alien Purple is noticeably lighter, more muted than Ultramarine.

Can I use Alien Purple instead of Ultramarine?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Alien Purple is noticeably lighter, more muted than Ultramarine.

Can I use Ultramarine instead of Alien Purple?

The same difference applies the other way round: Ultramarine is noticeably darker, more saturated.

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.