ΔE 14.8, fair: the same colour family, but not a straight swap. Light Rust is a little lighter, warmer than Chestnut Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Light Rust is a little lighter, warmer than Chestnut Brown.
The same difference applies the other way round: Chestnut Brown is a little darker, 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 Light Rust on the colour wheel
All matches: Chestnut Brown equivalents · Light Rust equivalents