ΔE 16.1, loose: different enough that you should pick on purpose. Quinacridone Magenta is a little lighter, more saturated, warmer than Witchbane Plum.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Quinacridone Magenta is a little lighter, more saturated, warmer than Witchbane Plum.
The same difference applies the other way round: Witchbane Plum 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.
See Witchbane Plum on the colour wheel See Quinacridone Magenta on the colour wheel
All matches: Witchbane Plum equivalents · Quinacridone Magenta equivalents