Nurgling Green vs Light Gray

How close are they?

ΔE 18.8, loose: different enough that you should pick on purpose. Light Gray is a little lighter, more muted, cooler than Nurgling Green.

Can I use Light Gray instead of Nurgling Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Light Gray is a little lighter, more muted, cooler than Nurgling Green.

Can I use Nurgling Green instead of Light Gray?

The same difference applies the other way round: Nurgling Green is a little darker, more saturated, 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.