ΔE 7.7, close: similar, with a visible difference side by side. Foul Green is a little lighter, warmer than Emerald.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Foul Green is a little lighter, warmer than Emerald.
The same difference applies the other way round: Emerald is a little darker, cooler.
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 Emerald on the colour wheel See Foul Green on the colour wheel
All matches: Emerald equivalents · Foul Green equivalents