ΔE 14.4, fair: the same colour family, but not a straight swap. Flat Brown is a little darker, cooler than Gorthor Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Flat Brown is a little darker, cooler than Gorthor Brown.
The same difference applies the other way round: Gorthor Brown is a little lighter, 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 Gorthor Brown on the colour wheel See Flat Brown on the colour wheel
All matches: Gorthor Brown equivalents · Flat Brown equivalents