Light Drab vs Nurgling Green

How close are they?

ΔE 9.1, close: similar, with a visible difference side by side. Nurgling Green is a little lighter, cooler than Light Drab.

Can I use Nurgling Green instead of Light Drab?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Nurgling Green is a little lighter, cooler than Light Drab.

Can I use Light Drab instead of Nurgling Green?

The same difference applies the other way round: Light Drab is a little darker, 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.