Arcane Purple vs Storm Blue

How close are they?

ΔE 22.9, loose: different enough that you should pick on purpose. Storm Blue is noticeably lighter, cooler than Arcane Purple.

Can I use Storm Blue instead of Arcane Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Storm Blue is noticeably lighter, cooler than Arcane Purple.

Can I use Arcane Purple instead of Storm Blue?

The same difference applies the other way round: Arcane Purple is noticeably darker, 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.