ΔE 10.4, fair: the same colour family, but not a straight swap. Rust is a little darker, cooler than Dark Earth.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Rust is a little darker, cooler than Dark Earth.
The same difference applies the other way round: Dark Earth 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 Dark Earth on the colour wheel See Rust on the colour wheel
All matches: Dark Earth equivalents · Rust equivalents