ΔE 10.3, fair: the same colour family, but not a straight swap. IJA Olive Green is a little darker, cooler than Drab Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). IJA Olive Green is a little darker, cooler than Drab Brown.
The same difference applies the other way round: Drab Brown is a little lighter, 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 Drab Brown on the colour wheel See IJA Olive Green on the colour wheel
All matches: Drab Brown equivalents · IJA Olive Green equivalents