ΔE 12.5, fair: the same colour family, but not a straight swap. Brown RLM26 is a little lighter, more muted than Dark Crimson.
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 lighter, more muted than Dark Crimson.
The same difference applies the other way round: Dark Crimson is a little darker, more saturated.
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 Dark Crimson on the colour wheel See Brown RLM26 on the colour wheel
All matches: Dark Crimson equivalents · Brown RLM26 equivalents