ΔE 10.5, fair: the same colour family, but not a straight swap. Catachan Flesh is a little lighter, warmer than Old Rust.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Catachan Flesh is a little lighter, warmer than Old Rust.
The same difference applies the other way round: Old Rust 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 Old Rust on the colour wheel See Catachan Flesh on the colour wheel
All matches: Old Rust equivalents · Catachan Flesh equivalents