Dusk Red vs Deep Purple

How close are they?

ΔE 20.5, loose: different enough that you should pick on purpose. Deep Purple is noticeably darker, cooler than Dusk Red.

Can I use Deep Purple instead of Dusk Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Deep Purple is noticeably darker, cooler than Dusk Red.

Can I use Dusk Red instead of Deep Purple?

The same difference applies the other way round: Dusk Red 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.