ΔE 10.6, fair: the same colour family, but not a straight swap. Deep Green is a little darker, more muted than Forest Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Deep Green is a little darker, more muted than Forest Green.
The same difference applies the other way round: Forest Green is a little 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 Forest Green on the colour wheel See Deep Green on the colour wheel
All matches: Forest Green equivalents · Deep Green equivalents