Idrian Flesh vs Grunge Brown

How close are they?

ΔE 17.3, loose: different enough that you should pick on purpose. Grunge Brown is a little lighter, much more saturated, cooler than Idrian Flesh.

Can I use Grunge Brown instead of Idrian Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Grunge Brown is a little lighter, much more saturated, cooler than Idrian Flesh.

Can I use Idrian Flesh instead of Grunge Brown?

The same difference applies the other way round: Idrian Flesh is a little darker, much more muted, 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.