Ultramarine Blue vs Beaten Purple

How close are they?

ΔE 21.8, loose: different enough that you should pick on purpose. Beaten Purple is a little darker, warmer than Ultramarine Blue.

Can I use Beaten Purple instead of Ultramarine Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Beaten Purple is a little darker, warmer than Ultramarine Blue.

Can I use Ultramarine Blue instead of Beaten Purple?

The same difference applies the other way round: Ultramarine Blue is a little lighter, 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.