Flayed One Flesh vs Resurrection Flesh

How close are they?

ΔE 9.8, close: similar, with a visible difference side by side. Resurrection Flesh is a little darker than Flayed One Flesh.

Can I use Resurrection Flesh instead of Flayed One Flesh?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Resurrection Flesh is a little darker than Flayed One Flesh.

Can I use Flayed One Flesh instead of Resurrection Flesh?

The same difference applies the other way round: Flayed One Flesh is a little lighter.

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.