Green-Grey vs Grotesque Green

How close are they?

ΔE 9.2, close: similar, with a visible difference side by side. Grotesque Green is a little darker than Green-Grey.

Can I use Grotesque Green instead of Green-Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Grotesque Green is a little darker than Green-Grey.

Can I use Green-Grey instead of Grotesque Green?

The same difference applies the other way round: Green-Grey 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.