ΔE 11.6, fair: the same colour family, but not a straight swap. Grey Brown is a little darker, more saturated, cooler than Drab Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Grey Brown is a little darker, more saturated, cooler than Drab Brown.
The same difference applies the other way round: Drab Brown is a little lighter, more muted, 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 Drab Brown on the colour wheel See Grey Brown on the colour wheel
All matches: Drab Brown equivalents · Grey Brown equivalents