Slaanesh Grey vs Runic Purple

How close are they?

ΔE 9.4, close: similar, with a visible difference side by side. Runic Purple is a little lighter, more saturated than Slaanesh Grey.

Can I use Runic Purple instead of Slaanesh Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Runic Purple is a little lighter, more saturated than Slaanesh Grey.

Can I use Slaanesh Grey instead of Runic Purple?

The same difference applies the other way round: Slaanesh Grey is a little darker, more muted.

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.