ΔE 27.7, loose: different enough that you should pick on purpose. Mahogany Ink is noticeably lighter, more saturated than Umber Ink.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Mahogany Ink is noticeably lighter, more saturated than Umber Ink.
The same difference applies the other way round: Umber Ink is noticeably darker, more muted.
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 Umber Ink on the colour wheel See Mahogany Ink on the colour wheel
All matches: Umber Ink equivalents · Mahogany Ink equivalents