Crusted Sore vs Dark Flesh

How close are they?

ΔE 16.3, loose: different enough that you should pick on purpose. Dark Flesh is more muted, warmer than Crusted Sore.

Can I use Dark Flesh instead of Crusted Sore?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Dark Flesh is more muted, warmer than Crusted Sore.

Can I use Crusted Sore instead of Dark Flesh?

The same difference applies the other way round: Crusted Sore is more saturated, 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.