Undead Flesh vs Desert Tan

How close are they?

ΔE 10.0, close: similar, with a visible difference side by side. Desert Tan is a little darker, more muted, warmer than Undead Flesh.

Can I use Desert Tan instead of Undead Flesh?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Desert Tan is a little darker, more muted, warmer than Undead Flesh.

Can I use Undead Flesh instead of Desert Tan?

The same difference applies the other way round: Undead Flesh is a little 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.