Slaanesh Grey vs Medium Seagray BS637

How close are they?

ΔE 15.6, loose: different enough that you should pick on purpose. Medium Seagray BS637 is more muted, cooler than Slaanesh Grey.

Can I use Medium Seagray BS637 instead of Slaanesh Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Medium Seagray BS637 is more muted, cooler than Slaanesh Grey.

Can I use Slaanesh Grey instead of Medium Seagray BS637?

The same difference applies the other way round: Slaanesh Grey is more saturated, 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.