Bright Yellow Ochre vs Natural Flesh

How close are they?

ΔE 18.8, loose: different enough that you should pick on purpose. Natural Flesh is noticeably lighter, more muted than Bright Yellow Ochre.

Can I use Natural Flesh instead of Bright Yellow Ochre?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Natural Flesh is noticeably lighter, more muted than Bright Yellow Ochre.

Can I use Bright Yellow Ochre instead of Natural Flesh?

The same difference applies the other way round: Bright Yellow Ochre is noticeably darker, more saturated.

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.