Underhive Ash vs Terran Khaki

How close are they?

ΔE 7.1, close: similar, with a visible difference side by side. Terran Khaki is more saturated, warmer than Underhive Ash.

Can I use Terran Khaki instead of Underhive Ash?

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

Can I use Underhive Ash instead of Terran Khaki?

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