Violet Coven vs Slaanesh Grey

How close are they?

ΔE 16.6, loose: different enough that you should pick on purpose. Slaanesh Grey is noticeably darker, more muted than Violet Coven.

Can I use Slaanesh Grey instead of Violet Coven?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Slaanesh Grey is noticeably darker, more muted than Violet Coven.

Can I use Violet Coven instead of Slaanesh Grey?

The same difference applies the other way round: Violet Coven is noticeably 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.