ΔE 11.9, fair: the same colour family, but not a straight swap. Fulgurite Copper is a little lighter than Rusty Brass.
Can I use Fulgurite Copper instead of Rusty Brass?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Fulgurite Copper is a little lighter than Rusty Brass.
Can I use Rusty Brass instead of Fulgurite Copper?
The same difference applies the other way round: Rusty Brass is a little darker.
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.