Purple vs Crimson

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Crimson is noticeably lighter, much more saturated than Purple.

Can I use Crimson instead of Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Crimson is noticeably lighter, much more saturated than Purple.

Can I use Purple instead of Crimson?

The same difference applies the other way round: Purple is noticeably darker, much more muted.

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.