Metallic Blue vs Celestial Violet

How close are they?

ΔE 27.8, loose: different enough that you should pick on purpose. Celestial Violet is a little lighter, warmer than Metallic Blue.

Can I use Celestial Violet instead of Metallic Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Celestial Violet is a little lighter, warmer than Metallic Blue.

Can I use Metallic Blue instead of Celestial Violet?

The same difference applies the other way round: Metallic Blue is a little darker, 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.