Underhive Ash vs Cloudy Sky

How close are they?

ΔE 19.7, loose: different enough that you should pick on purpose. Cloudy Sky is noticeably lighter, more saturated, warmer than Underhive Ash.

Can I use Cloudy Sky instead of Underhive Ash?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Cloudy Sky is noticeably lighter, more saturated, warmer than Underhive Ash.

Can I use Underhive Ash instead of Cloudy Sky?

The same difference applies the other way round: Underhive Ash is noticeably darker, 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.