ΔE 13.1, fair: the same colour family, but not a straight swap. Olive Drab is a little darker, more saturated, warmer than Army Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Olive Drab is a little darker, more saturated, warmer than Army Green.
The same difference applies the other way round: Army Green is a little lighter, more muted, 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 Army Green on the colour wheel See Olive Drab on the colour wheel
All matches: Army Green equivalents · Olive Drab equivalents