ΔE 10.1, fair: the same colour family, but not a straight swap. Dark Flesh Tone is a little darker, more saturated, warmer than Rust Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Dark Flesh Tone is a little darker, more saturated, warmer than Rust Brown.
The same difference applies the other way round: Rust Brown is a little lighter, more muted, 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 Rust Brown on the colour wheel See Dark Flesh Tone on the colour wheel
All matches: Rust Brown equivalents · Dark Flesh Tone equivalents