ΔE 10.5, fair: the same colour family, but not a straight swap. Violet Grey is more saturated, cooler than Slaanesh Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Violet Grey is more saturated, cooler than Slaanesh Grey.
The same difference applies the other way round: Slaanesh 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 Slaanesh Grey on the colour wheel See Violet Grey on the colour wheel
All matches: Slaanesh Grey equivalents · Violet Grey equivalents