Barren Dune vs Cloudy Sky

How close are they?

ΔE 26.3, loose: different enough that you should pick on purpose. Cloudy Sky is a little lighter, much more muted, warmer than Barren Dune.

Can I use Cloudy Sky instead of Barren Dune?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Cloudy Sky is a little lighter, much more muted, warmer than Barren Dune.

Can I use Barren Dune instead of Cloudy Sky?

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