ΔE 22.6, loose: different enough that you should pick on purpose. Deck Grey is noticeably lighter, more muted, warmer than Necrotic Flesh.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Deck Grey is noticeably lighter, more muted, warmer than Necrotic Flesh.
The same difference applies the other way round: Necrotic Flesh 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.
See Necrotic Flesh on the colour wheel See Deck Grey on the colour wheel
All matches: Necrotic Flesh equivalents · Deck Grey equivalents