ΔE 12.3, fair: the same colour family, but not a straight swap. Firethorn Brown is more muted, warmer than Imperial Red.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Firethorn Brown is more muted, warmer than Imperial Red.
The same difference applies the other way round: Imperial Red is more saturated, cooler.
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 Imperial Red on the colour wheel See Firethorn Brown on the colour wheel
All matches: Imperial Red equivalents · Firethorn Brown equivalents