Orc Flesh vs Dark Green

How close are they?

ΔE 19.1, loose: different enough that you should pick on purpose. Dark Green is noticeably darker, more muted, cooler than Orc Flesh.

Can I use Dark Green instead of Orc Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Dark Green is noticeably darker, more muted, cooler than Orc Flesh.

Can I use Orc Flesh instead of Dark Green?

The same difference applies the other way round: Orc Flesh is noticeably lighter, more saturated, warmer.

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.