Screaming Skull vs 'Jack Bone

How close are they?

ΔE 9.4, close: similar, with a visible difference side by side. 'Jack Bone is more saturated, cooler than Screaming Skull.

Can I use 'Jack Bone instead of Screaming Skull?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). 'Jack Bone is more saturated, cooler than Screaming Skull.

Can I use Screaming Skull instead of 'Jack Bone?

The same difference applies the other way round: Screaming Skull is more muted, 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.