Imperium Blue vs Imperial Purple

How close are they?

ΔE 28.0, loose: different enough that you should pick on purpose. Imperial Purple is noticeably lighter, warmer than Imperium Blue.

Can I use Imperial Purple instead of Imperium Blue?

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

Can I use Imperium Blue instead of Imperial Purple?

The same difference applies the other way round: Imperium Blue is noticeably darker, cooler.

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.