Darkoath Flesh vs Papyrus

How close are they?

ΔE 21.8, loose: different enough that you should pick on purpose. Papyrus is noticeably darker, cooler than Darkoath Flesh.

Can I use Papyrus instead of Darkoath Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Papyrus is noticeably darker, cooler than Darkoath Flesh.

Can I use Darkoath Flesh instead of Papyrus?

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