ΔE 11.3, fair: the same colour family, but not a straight swap. Rust Brown is a little darker, more saturated, cooler than Ruddy Umber.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Rust Brown is a little darker, more saturated, cooler than Ruddy Umber.
The same difference applies the other way round: Ruddy Umber is a little lighter, more muted, 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 Ruddy Umber on the colour wheel See Rust Brown on the colour wheel
All matches: Ruddy Umber equivalents · Rust Brown equivalents