Arid Earth vs Tyrant Skull

How close are they?

ΔE 16.8, loose: different enough that you should pick on purpose. Tyrant Skull is noticeably darker, much more muted than Arid Earth.

Can I use Tyrant Skull instead of Arid Earth?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Tyrant Skull is noticeably darker, much more muted than Arid Earth.

Can I use Arid Earth instead of Tyrant Skull?

The same difference applies the other way round: Arid Earth is noticeably lighter, much more saturated.

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.