ΔE 12.6, fair: the same colour family, but not a straight swap. IJA Gray is much more muted than Potion Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). IJA Gray is much more muted than Potion Green.
The same difference applies the other way round: Potion Green is much more saturated.
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 Potion Green on the colour wheel See IJA Gray on the colour wheel
All matches: Potion Green equivalents · IJA Gray equivalents