ΔE 18.6, loose: different enough that you should pick on purpose. Green Brown is a little darker, more saturated, cooler than Walnut.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Green Brown is a little darker, more saturated, cooler than Walnut.
The same difference applies the other way round: Walnut 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 Walnut on the colour wheel See Green Brown on the colour wheel
All matches: Walnut equivalents · Green Brown equivalents