ΔE 17.2, loose: different enough that you should pick on purpose. Caspian Flesh Wash is noticeably lighter, more saturated, warmer than Mortarion Grime.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Caspian Flesh Wash is noticeably lighter, more saturated, warmer than Mortarion Grime.
The same difference applies the other way round: Mortarion Grime is noticeably darker, more muted, 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.
See Mortarion Grime on the colour wheel See Caspian Flesh Wash on the colour wheel
All matches: Mortarion Grime equivalents · Caspian Flesh Wash equivalents