ΔE 32.4, loose: different enough that you should pick on purpose. Pearl Blue is a little lighter, more muted, cooler than Royal Purple. They are different kinds of paint: Army Painter Royal Purple is a metallic and Tamiya Pearl Blue is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Pearl Blue is a little lighter, more muted, cooler than Royal Purple. They are different kinds of paint.
The same difference applies the other way round: Royal Purple is a little darker, 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 Pearl Blue on the colour wheel
All matches: Royal Purple equivalents · Pearl Blue equivalents