ΔE 10.7, fair: the same colour family, but not a straight swap. USAF Medium Gray is a little darker, more muted than Slaanesh Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). USAF Medium Gray is a little darker, more muted than Slaanesh Grey.
The same difference applies the other way round: Slaanesh Grey is a little lighter, more saturated.
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 USAF Medium Gray on the colour wheel
All matches: Slaanesh Grey equivalents · USAF Medium Gray equivalents