Flayed One Flesh vs Cloudy Sky

How close are they?

ΔE 16.5, loose: different enough that you should pick on purpose. Cloudy Sky is noticeably lighter, more muted, cooler than Flayed One Flesh.

Can I use Cloudy Sky instead of Flayed One Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Cloudy Sky is noticeably lighter, more muted, cooler than Flayed One Flesh.

Can I use Flayed One Flesh instead of Cloudy Sky?

The same difference applies the other way round: Flayed One Flesh is noticeably darker, 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.