ΔE 12.1, fair: the same colour family, but not a straight swap. Flat Brown is a little darker, more muted than Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Flat Brown is a little darker, more muted than Brown.
The same difference applies the other way round: Brown 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 Brown on the colour wheel See Flat Brown on the colour wheel
All matches: Brown equivalents · Flat Brown equivalents