Peachy Flesh vs Aggaros Dunes

How close are they?

ΔE 19.8, loose: different enough that you should pick on purpose. Aggaros Dunes is a little darker, cooler than Peachy Flesh.

Can I use Aggaros Dunes instead of Peachy Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Aggaros Dunes is a little darker, cooler than Peachy Flesh.

Can I use Peachy Flesh instead of Aggaros Dunes?

The same difference applies the other way round: Peachy Flesh is a little lighter, 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.