Tyrant Skull vs Ivory

How close are they?

ΔE 9.4, close: similar, with a visible difference side by side. Ivory is a little lighter, more muted than Tyrant Skull.

Can I use Ivory instead of Tyrant Skull?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Ivory is a little lighter, more muted than Tyrant Skull.

Can I use Tyrant Skull instead of Ivory?

The same difference applies the other way round: Tyrant Skull is a little darker, 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.