ΔE 11.7, fair: the same colour family, but not a straight swap. Brown RLM26 is a little darker, more muted, cooler than Dull Red.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Brown RLM26 is a little darker, more muted, cooler than Dull Red.
The same difference applies the other way round: Dull Red is a little lighter, more saturated, warmer.
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 Dull Red on the colour wheel See Brown RLM26 on the colour wheel
All matches: Dull Red equivalents · Brown RLM26 equivalents