ΔE 19.6, loose: different enough that you should pick on purpose. Plum is noticeably lighter, more muted, warmer than Xereus Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Plum is noticeably lighter, more muted, warmer than Xereus Purple.
The same difference applies the other way round: Xereus Purple is noticeably darker, more saturated, 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 Xereus Purple on the colour wheel See Plum on the colour wheel
All matches: Xereus Purple equivalents · Plum equivalents