Mutant Hue vs Ryn Flesh

How close are they?

ΔE 21.2, loose: different enough that you should pick on purpose. Ryn Flesh is a little lighter, warmer than Mutant Hue.

Can I use Ryn Flesh instead of Mutant Hue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Ryn Flesh is a little lighter, warmer than Mutant Hue.

Can I use Mutant Hue instead of Ryn Flesh?

The same difference applies the other way round: Mutant Hue is a little darker, 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.