Crystal Blue vs Beaten Purple

How close are they?

ΔE 38.4, loose: different enough that you should pick on purpose. Beaten Purple is noticeably darker, warmer than Crystal Blue.

Can I use Beaten Purple instead of Crystal Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 38). Beaten Purple is noticeably darker, warmer than Crystal Blue.

Can I use Crystal Blue instead of Beaten Purple?

The same difference applies the other way round: Crystal Blue is noticeably 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.