Magenta vs Amethyst

How close are they?

ΔE 18.2, loose: different enough that you should pick on purpose. Amethyst is more muted, cooler than Magenta.

Can I use Amethyst instead of Magenta?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Amethyst is more muted, cooler than Magenta.

Can I use Magenta instead of Amethyst?

The same difference applies the other way round: Magenta is more saturated, warmer.

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.