Stone Grey vs Ryn Flesh

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Ryn Flesh is noticeably lighter, warmer than Stone Grey.

Can I use Ryn Flesh instead of Stone Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Ryn Flesh is noticeably lighter, warmer than Stone Grey.

Can I use Stone Grey instead of Ryn Flesh?

The same difference applies the other way round: Stone Grey is noticeably 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.