ΔE 12.9, fair: the same colour family, but not a straight swap. Crimson is a little lighter, more saturated than Red Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Crimson is a little lighter, more saturated than Red Purple.
The same difference applies the other way round: Red Purple is a little darker, 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.
See Red Purple on the colour wheel See Crimson on the colour wheel
All matches: Red Purple equivalents · Crimson equivalents