Green-Grey vs Screaming Skull

How close are they?

ΔE 8.5, close: similar, with a visible difference side by side. Screaming Skull is a little darker, warmer than Green-Grey.

Can I use Screaming Skull instead of Green-Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Screaming Skull is a little darker, warmer than Green-Grey.

Can I use Green-Grey instead of Screaming Skull?

The same difference applies the other way round: Green-Grey is a little lighter, cooler.

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.