Luminous Flesh vs Flayed One Flesh

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Flayed One Flesh is a little darker, more muted, warmer than Luminous Flesh.

Can I use Flayed One Flesh instead of Luminous Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Flayed One Flesh is a little darker, more muted, warmer than Luminous Flesh.

Can I use Luminous Flesh instead of Flayed One Flesh?

The same difference applies the other way round: Luminous 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.