Dusty Skull vs Thornwood Green

How close are they?

ΔE 18.5, loose: different enough that you should pick on purpose. Thornwood Green is noticeably darker, cooler than Dusty Skull.

Can I use Thornwood Green instead of Dusty Skull?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Thornwood Green is noticeably darker, cooler than Dusty Skull.

Can I use Dusty Skull instead of Thornwood Green?

The same difference applies the other way round: Dusty Skull is noticeably lighter, 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.