ΔE 13.3, fair: the same colour family, but not a straight swap. Olivegrove Green is noticeably darker, more muted than Helmet Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Olivegrove Green is noticeably darker, more muted than Helmet Brown.
The same difference applies the other way round: Helmet Brown is noticeably lighter, more saturated.
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 Helmet Brown on the colour wheel See Olivegrove Green on the colour wheel
All matches: Helmet Brown equivalents · Olivegrove Green equivalents