Cerulean Blue, Chromium vs Alien Purple

How close are they?

ΔE 16.3, loose: different enough that you should pick on purpose. Alien Purple is more muted, warmer than Cerulean Blue, Chromium.

Can I use Alien Purple instead of Cerulean Blue, Chromium?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Alien Purple is more muted, warmer than Cerulean Blue, Chromium.

Can I use Cerulean Blue, Chromium instead of Alien Purple?

The same difference applies the other way round: Cerulean Blue, Chromium is more saturated, 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.