Noble Skin vs Rotten Flesh

How close are they?

ΔE 16.5, loose: different enough that you should pick on purpose. Rotten Flesh is a little lighter, much more saturated than Noble Skin.

Can I use Rotten Flesh instead of Noble Skin?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Rotten Flesh is a little lighter, much more saturated than Noble Skin.

Can I use Noble Skin instead of Rotten Flesh?

The same difference applies the other way round: Noble Skin is a little darker, much more muted.

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.