Darkoath Flesh vs Rage Brown

How close are they?

ΔE 25.2, loose: different enough that you should pick on purpose. Rage Brown is noticeably darker, more saturated, cooler than Darkoath Flesh.

Can I use Rage Brown instead of Darkoath Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Rage Brown is noticeably darker, more saturated, cooler than Darkoath Flesh.

Can I use Darkoath Flesh instead of Rage Brown?

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