ΔE 10.3, fair: the same colour family, but not a straight swap. Rust is a little darker, more saturated than Smoke Gray.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Rust is a little darker, more saturated than Smoke Gray.
The same difference applies the other way round: Smoke Gray is a little 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 Smoke Gray on the colour wheel See Rust on the colour wheel
All matches: Smoke Gray equivalents · Rust equivalents