ΔE 59.6, loose: different enough that you should pick on purpose. Umber Wash is noticeably lighter, much more muted, warmer than Magenta Wash.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 60). Umber Wash is noticeably lighter, much more muted, warmer than Magenta Wash.
The same difference applies the other way round: Magenta Wash is noticeably darker, much 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 Magenta Wash on the colour wheel See Umber Wash on the colour wheel
All matches: Magenta Wash equivalents · Umber Wash equivalents