ΔE 13.7, fair: the same colour family, but not a straight swap. Cold Armour is noticeably darker, cooler than Slaanesh Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Cold Armour is noticeably darker, cooler than Slaanesh Grey.
The same difference applies the other way round: Slaanesh Grey is noticeably lighter, 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 Cold Armour on the colour wheel
All matches: Slaanesh Grey equivalents · Cold Armour equivalents