ΔE 9.0, close: similar, with a visible difference side by side. Camo Brown is a little darker, cooler than Old Rust.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Camo Brown is a little darker, cooler than Old Rust.
The same difference applies the other way round: Old Rust 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 Old Rust on the colour wheel See Camo Brown on the colour wheel
All matches: Old Rust equivalents · Camo Brown equivalents