ΔE 11.7, fair: the same colour family, but not a straight swap. Dark Rust is a little darker, more saturated than Blackroot Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Dark Rust is a little darker, more saturated than Blackroot Grey.
The same difference applies the other way round: Blackroot Grey 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 Blackroot Grey on the colour wheel See Dark Rust on the colour wheel
All matches: Blackroot Grey equivalents · Dark Rust equivalents