ΔE 12.6, fair: the same colour family, but not a straight swap. Grey Brown is noticeably darker, more muted than Green Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Grey Brown is noticeably darker, more muted than Green Brown.
The same difference applies the other way round: Green 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 Green Brown on the colour wheel See Grey Brown on the colour wheel
All matches: Green Brown equivalents · Grey Brown equivalents