Plum vs Magenta

How close are they?

ΔE 19.4, loose: different enough that you should pick on purpose. Magenta is a little darker, warmer than Plum.

Can I use Magenta instead of Plum?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Magenta is a little darker, warmer than Plum.

Can I use Plum instead of Magenta?

The same difference applies the other way round: Plum is a little lighter, 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.