Galaxia vs Celestial Violet

How close are they?

ΔE 16.2, loose: different enough that you should pick on purpose. Celestial Violet is noticeably lighter, more muted, warmer than Galaxia.

Can I use Celestial Violet instead of Galaxia?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Celestial Violet is noticeably lighter, more muted, warmer than Galaxia.

Can I use Galaxia instead of Celestial Violet?

The same difference applies the other way round: Galaxia is noticeably darker, 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.