ΔE 11.7, fair: the same colour family, but not a straight swap. Runelord Brass is more saturated than True Brass.
Can I use Runelord Brass instead of True Brass?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Runelord Brass is more saturated than True Brass.
Can I use True Brass instead of Runelord Brass?
The same difference applies the other way round: True Brass is 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.