Medium Sea Grey vs Underhive Ash

How close are they?

ΔE 7.8, close: similar, with a visible difference side by side. Underhive Ash is a little lighter than Medium Sea Grey.

Can I use Underhive Ash instead of Medium Sea Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Underhive Ash is a little lighter than Medium Sea Grey.

Can I use Medium Sea Grey instead of Underhive Ash?

The same difference applies the other way round: Medium Sea Grey is a little darker.

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.