Purple Rain vs Macragge Blue

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Macragge Blue is noticeably darker, cooler than Purple Rain.

Can I use Macragge Blue instead of Purple Rain?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Macragge Blue is noticeably darker, cooler than Purple Rain.

Can I use Purple Rain instead of Macragge Blue?

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