Purple Rain vs Magic Blue

How close are they?

ΔE 28.1, loose: different enough that you should pick on purpose. Magic Blue is noticeably lighter, cooler than Purple Rain.

Can I use Magic Blue instead of Purple Rain?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Magic Blue is noticeably lighter, cooler than Purple Rain.

Can I use Purple Rain instead of Magic Blue?

The same difference applies the other way round: Purple Rain 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.