Oblivion Black Wash vs Umber Wash

How close are they?

ΔE 8.6, close: similar, with a visible difference side by side. Umber Wash is more saturated than Oblivion Black Wash.

Can I use Umber Wash instead of Oblivion Black Wash?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Umber Wash is more saturated than Oblivion Black Wash.

Can I use Oblivion Black Wash instead of Umber Wash?

The same difference applies the other way round: Oblivion Black Wash is 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.