ΔE 18.4, loose: different enough that you should pick on purpose. Gorgon Brown is a little lighter, much more saturated, warmer than Chestnut Brown.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Gorgon Brown is a little lighter, much more saturated, warmer than Chestnut Brown.
The same difference applies the other way round: Chestnut Brown is a little darker, much more muted, cooler.
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 Chestnut Brown on the colour wheel See Gorgon Brown on the colour wheel
All matches: Chestnut Brown equivalents · Gorgon Brown equivalents