Desolate Brown vs Papyrus

How close are they?

ΔE 18.6, loose: different enough that you should pick on purpose. Papyrus is noticeably darker, more muted, warmer than Desolate Brown.

Can I use Papyrus instead of Desolate Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Papyrus is noticeably darker, more muted, warmer than Desolate Brown.

Can I use Desolate Brown instead of Papyrus?

The same difference applies the other way round: Desolate Brown is noticeably lighter, more saturated, 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.