ΔE 24.7, loose: different enough that you should pick on purpose. Flesh Wash is a little darker, warmer than Necrosis Green Wash.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Flesh Wash is a little darker, warmer than Necrosis Green Wash.
The same difference applies the other way round: Necrosis Green Wash is a little lighter, 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 Necrosis Green Wash on the colour wheel See Flesh Wash on the colour wheel
All matches: Necrosis Green Wash equivalents · Flesh Wash equivalents