Metallic Purple vs Amethyst Purple

How close are they?

ΔE 23.5, loose: different enough that you should pick on purpose. Amethyst Purple is noticeably lighter, warmer than Metallic Purple.

Can I use Amethyst Purple instead of Metallic Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Amethyst Purple is noticeably lighter, warmer than Metallic Purple.

Can I use Metallic Purple instead of Amethyst Purple?

The same difference applies the other way round: Metallic Purple is noticeably 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.