Flesh Wash vs Necrosis Green Wash

How close are they?

ΔE 16.0, loose: different enough that you should pick on purpose. Necrosis Green Wash is a little darker, cooler than Flesh Wash.

Can I use Necrosis Green Wash instead of Flesh Wash?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Necrosis Green Wash is a little darker, cooler than Flesh Wash.

Can I use Flesh Wash instead of Necrosis Green Wash?

The same difference applies the other way round: Flesh Wash is a little lighter, warmer.

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.