Howling Sand vs Zombie Skin

How close are they?

ΔE 24.9, loose: different enough that you should pick on purpose. Zombie Skin is noticeably darker, much more saturated than Howling Sand.

Can I use Zombie Skin instead of Howling Sand?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Zombie Skin is noticeably darker, much more saturated than Howling Sand.

Can I use Howling Sand instead of Zombie Skin?

The same difference applies the other way round: Howling Sand is noticeably lighter, much more muted.

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.