Nomad Flesh vs Idrian Flesh

How close are they?

ΔE 18.5, loose: different enough that you should pick on purpose. Idrian Flesh is noticeably darker, more muted, warmer than Nomad Flesh.

Can I use Idrian Flesh instead of Nomad Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Idrian Flesh is noticeably darker, more muted, warmer than Nomad Flesh.

Can I use Nomad Flesh instead of Idrian Flesh?

The same difference applies the other way round: Nomad Flesh is noticeably lighter, 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.