Underhive Ash vs Beige Grey

How close are they?

ΔE 6.7, close: similar, with a visible difference side by side. Beige Grey is more muted, warmer than Underhive Ash.

Can I use Beige Grey instead of Underhive Ash?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Beige Grey is more muted, warmer than Underhive Ash.

Can I use Underhive Ash instead of Beige Grey?

The same difference applies the other way round: Underhive Ash is more saturated, cooler.

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.