ΔE 12.6, fair: the same colour family, but not a straight swap. Brown Skin is noticeably darker, more saturated than Rust.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Brown Skin is noticeably darker, more saturated than Rust.
The same difference applies the other way round: Rust is noticeably lighter, more muted.
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 Rust on the colour wheel See Brown Skin on the colour wheel
All matches: Rust equivalents · Brown Skin equivalents