Desert Sand vs Fairy Flesh

How close are they?

ΔE 17.5, loose: different enough that you should pick on purpose. Fairy Flesh is a little darker, more saturated, warmer than Desert Sand.

Can I use Fairy Flesh instead of Desert Sand?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Fairy Flesh is a little darker, more saturated, warmer than Desert Sand.

Can I use Desert Sand instead of Fairy Flesh?

The same difference applies the other way round: Desert Sand is a little lighter, 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.