Skeleton Horde vs Human Flesh

How close are they?

ΔE 22.7, loose: different enough that you should pick on purpose. Human Flesh is a little darker, more muted, warmer than Skeleton Horde.

Can I use Human Flesh instead of Skeleton Horde?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Human Flesh is a little darker, more muted, warmer than Skeleton Horde.

Can I use Skeleton Horde instead of Human Flesh?

The same difference applies the other way round: Skeleton Horde is a little lighter, 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.