ΔE 13.5, fair: the same colour family, but not a straight swap. Forest Green is a little lighter, more saturated, warmer than Dark Drab.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Forest Green is a little lighter, more saturated, warmer than Dark Drab.
The same difference applies the other way round: Dark Drab is a little darker, 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 Dark Drab on the colour wheel See Forest Green on the colour wheel
All matches: Dark Drab equivalents · Forest Green equivalents