ΔE 8.8, close: similar, with a visible difference side by side. Necrotic Flesh is more saturated, cooler than Rock Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Necrotic Flesh is more saturated, cooler than Rock Grey.
The same difference applies the other way round: Rock Grey is more muted, 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.
See Rock Grey on the colour wheel See Necrotic Flesh on the colour wheel
All matches: Rock Grey equivalents · Necrotic Flesh equivalents