Permanent Violet Dark vs Imperial Purple

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Imperial Purple is noticeably lighter, cooler than Permanent Violet Dark.

Can I use Imperial Purple instead of Permanent Violet Dark?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Imperial Purple is noticeably lighter, cooler than Permanent Violet Dark.

Can I use Permanent Violet Dark instead of Imperial Purple?

The same difference applies the other way round: Permanent Violet Dark 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.