ΔE 12.1, fair: the same colour family, but not a straight swap. IJA Olive Green is a little lighter, more muted, cooler than Olive-Brown Ops.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). IJA Olive Green is a little lighter, more muted, cooler than Olive-Brown Ops.
The same difference applies the other way round: Olive-Brown Ops is a little darker, more saturated, 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 Olive-Brown Ops on the colour wheel See IJA Olive Green on the colour wheel
All matches: Olive-Brown Ops equivalents · IJA Olive Green equivalents