Metallic Purple vs Celestial Violet

How close are they?

ΔE 29.3, loose: different enough that you should pick on purpose. Celestial Violet is noticeably darker, warmer than Metallic Purple.

Can I use Celestial Violet instead of Metallic Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Celestial Violet is noticeably darker, warmer than Metallic Purple.

Can I use Metallic Purple instead of Celestial Violet?

The same difference applies the other way round: Metallic Purple 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.