ΔE 11.9, fair: the same colour family, but not a straight swap. Slaanesh Grey is a little lighter, cooler than Vampire Flesh.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Slaanesh Grey is a little lighter, cooler than Vampire Flesh.
The same difference applies the other way round: Vampire Flesh is a little darker, 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 Vampire Flesh on the colour wheel See Slaanesh Grey on the colour wheel
All matches: Vampire Flesh equivalents · Slaanesh Grey equivalents