Purple vs Amethyst

How close are they?

ΔE 17.4, loose: different enough that you should pick on purpose. Amethyst is a little lighter, more saturated, warmer than Purple.

Can I use Amethyst instead of Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Amethyst is a little lighter, more saturated, warmer than Purple.

Can I use Purple instead of Amethyst?

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