Doombull Brown vs Umbral Umber

How close are they?

ΔE 26.3, loose: different enough that you should pick on purpose. Umbral Umber is noticeably darker, much more muted, warmer than Doombull Brown.

Can I use Umbral Umber instead of Doombull Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Umbral Umber is noticeably darker, much more muted, warmer than Doombull Brown.

Can I use Doombull Brown instead of Umbral Umber?

The same difference applies the other way round: Doombull Brown is noticeably lighter, 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.