Persian Violet vs Celestial Violet

How close are they?

ΔE 18.2, loose: different enough that you should pick on purpose. Celestial Violet is noticeably darker, more muted than Persian Violet.

Can I use Celestial Violet instead of Persian Violet?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Celestial Violet is noticeably darker, more muted than Persian Violet.

Can I use Persian Violet instead of Celestial Violet?

The same difference applies the other way round: Persian Violet is noticeably lighter, more saturated.

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.