ΔE 6.3, close: similar, with a visible difference side by side. Chestnut Brown is more saturated, warmer than Dark Leather.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Chestnut Brown is more saturated, warmer than Dark Leather.
The same difference applies the other way round: Dark Leather is 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 Dark Leather on the colour wheel See Chestnut Brown on the colour wheel
All matches: Dark Leather equivalents · Chestnut Brown equivalents