ΔE 8.9, close: similar, with a visible difference side by side. Grotesque Green is a little darker than Rotten Green.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Grotesque Green is a little darker than Rotten Green.
The same difference applies the other way round: Rotten 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.
See Rotten Green on the colour wheel See Grotesque Green on the colour wheel
All matches: Rotten Green equivalents · Grotesque Green equivalents