ΔE 24.9, loose: different enough that you should pick on purpose. Storm Blue is much more muted, cooler than Royal Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Storm Blue is much more muted, cooler than Royal Purple.
The same difference applies the other way round: Royal Purple is much 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 Royal Purple on the colour wheel See Storm Blue on the colour wheel
All matches: Royal Purple equivalents · Storm Blue equivalents