Underhive Ash vs Hammerfall Khaki

How close are they?

ΔE 17.2, loose: different enough that you should pick on purpose. Hammerfall Khaki is a little lighter, much more saturated than Underhive Ash.

Can I use Hammerfall Khaki instead of Underhive Ash?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Hammerfall Khaki is a little lighter, much more saturated than Underhive Ash.

Can I use Underhive Ash instead of Hammerfall Khaki?

The same difference applies the other way round: Underhive Ash is a little darker, much 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.