ΔE 12.9, fair: the same colour family, but not a straight swap. Greatcoat Green is more muted, warmer than Olive Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Greatcoat Green is more muted, warmer than Olive Green.
The same difference applies the other way round: Olive Green is 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 Olive Green on the colour wheel See Greatcoat Green on the colour wheel
All matches: Olive Green equivalents · Greatcoat Green equivalents