Diabolic Plum vs Sorcerer's Cloak

How close are they?

ΔE 23.3, loose: different enough that you should pick on purpose. Sorcerer's Cloak is noticeably lighter, much more muted, cooler than Diabolic Plum.

Can I use Sorcerer's Cloak instead of Diabolic Plum?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Sorcerer's Cloak is noticeably lighter, much more muted, cooler than Diabolic Plum.

Can I use Diabolic Plum instead of Sorcerer's Cloak?

The same difference applies the other way round: Diabolic Plum is noticeably darker, much more saturated, 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.