ΔE 16.2, loose: different enough that you should pick on purpose. Purple Black is a little lighter, more muted than Dark Rust.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Purple Black is a little lighter, more muted than Dark Rust.
The same difference applies the other way round: Dark Rust is a little darker, more saturated.
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 Dark Rust on the colour wheel See Purple Black on the colour wheel
All matches: Dark Rust equivalents · Purple Black equivalents