Yellow Sand vs Natural Flesh

How close are they?

ΔE 22.8, loose: different enough that you should pick on purpose. Natural Flesh is noticeably lighter, more saturated than Yellow Sand.

Can I use Natural Flesh instead of Yellow Sand?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Natural Flesh is noticeably lighter, more saturated than Yellow Sand.

Can I use Yellow Sand instead of Natural Flesh?

The same difference applies the other way round: Yellow Sand is noticeably darker, more muted.

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.