Amethyst vs Magecast Magenta

How close are they?

ΔE 15.3, loose: different enough that you should pick on purpose. Magecast Magenta is noticeably darker, more muted, cooler than Amethyst.

Can I use Magecast Magenta instead of Amethyst?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Magecast Magenta is noticeably darker, more muted, cooler than Amethyst.

Can I use Amethyst instead of Magecast Magenta?

The same difference applies the other way round: Amethyst is noticeably lighter, 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.