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