ΔE 24.3, loose: different enough that you should pick on purpose. Foul Green is a little lighter, much more saturated, cooler than Light Gray.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Foul Green is a little lighter, much more saturated, cooler than Light Gray.
The same difference applies the other way round: Light Gray is a little darker, much more muted, 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.
See Light Gray on the colour wheel See Foul Green on the colour wheel
All matches: Light Gray equivalents · Foul Green equivalents