Fur Brown vs Idrian Flesh

How close are they?

ΔE 19.7, loose: different enough that you should pick on purpose. Idrian Flesh is a little lighter, much more saturated, warmer than Fur Brown.

Can I use Idrian Flesh instead of Fur Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Idrian Flesh is a little lighter, much more saturated, warmer than Fur Brown.

Can I use Fur Brown instead of Idrian Flesh?

The same difference applies the other way round: Fur Brown is a little darker, much 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.