ΔE 9.6, close: similar, with a visible difference side by side. Plague Brown is a little darker, more muted than Light Rust.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Plague Brown is a little darker, more muted than Light Rust.
The same difference applies the other way round: Light Rust is a little lighter, more saturated.
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 Light Rust on the colour wheel See Plague Brown on the colour wheel
All matches: Light Rust equivalents · Plague Brown equivalents