ΔE 9.9, close: similar, with a visible difference side by side. Pale Green is a little darker than Nurgling Green.
Can I use Pale Green instead of Nurgling Green?
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Pale Green is a little darker than Nurgling Green.
Can I use Nurgling Green instead of Pale Green?
The same difference applies the other way round: Nurgling Green is a little lighter.
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.