Slaanesh Grey vs Warm Grey

How close are they?

ΔE 17.8, loose: different enough that you should pick on purpose. Warm Grey is a little darker, more muted than Slaanesh Grey.

Can I use Warm Grey instead of Slaanesh Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Warm Grey is a little darker, more muted than Slaanesh Grey.

Can I use Slaanesh Grey instead of Warm 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.