ΔE 16.4, loose: different enough that you should pick on purpose. Dark Purple is a little lighter, cooler than Umbral Umber.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Dark Purple is a little lighter, cooler than Umbral Umber.
The same difference applies the other way round: Umbral Umber is a little darker, 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.
See Umbral Umber on the colour wheel See Dark Purple on the colour wheel
All matches: Umbral Umber equivalents · Dark Purple equivalents