Chaotic Red vs Idrian Flesh

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. Idrian Flesh is noticeably lighter, warmer than Chaotic Red.

Can I use Idrian Flesh instead of Chaotic Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Idrian Flesh is noticeably lighter, warmer than Chaotic Red.

Can I use Chaotic Red instead of Idrian Flesh?

The same difference applies the other way round: Chaotic Red is noticeably darker, 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.