ΔE 11.5, fair: the same colour family, but not a straight swap. Royal Blue is a little darker, cooler than Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Royal Blue is a little darker, cooler than Purple.
The same difference applies the other way round: Purple is a little lighter, 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 Purple on the colour wheel See Royal Blue on the colour wheel
All matches: Purple equivalents · Royal Blue equivalents