Hearthborn vs Cloudy Sky

How close are they?

ΔE 20.2, loose: different enough that you should pick on purpose. Cloudy Sky is a little lighter, much more muted, cooler than Hearthborn.

Can I use Cloudy Sky instead of Hearthborn?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Cloudy Sky is a little lighter, much more muted, cooler than Hearthborn.

Can I use Hearthborn instead of Cloudy Sky?

The same difference applies the other way round: Hearthborn is a little darker, much more saturated, warmer.

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.