Mortarion Grime vs Umber Wash

How close are they?

ΔE 19.5, loose: different enough that you should pick on purpose. Umber Wash is noticeably lighter, more muted, warmer than Mortarion Grime.

Can I use Umber Wash instead of Mortarion Grime?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Umber Wash is noticeably lighter, more muted, warmer than Mortarion Grime.

Can I use Mortarion Grime instead of Umber Wash?

The same difference applies the other way round: Mortarion Grime is noticeably darker, 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.