ΔE 18.9, loose: different enough that you should pick on purpose. Pestilence Green is a little lighter, much more saturated, cooler than Screaming Skull.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Pestilence Green is a little lighter, much more saturated, cooler than Screaming Skull.
The same difference applies the other way round: Screaming Skull is a little darker, much 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.
See Screaming Skull on the colour wheel See Pestilence Green on the colour wheel
All matches: Screaming Skull equivalents · Pestilence Green equivalents