Cultist Purple vs Marine Blue

How close are they?

ΔE 20.0, loose: different enough that you should pick on purpose. Marine Blue is noticeably darker, more saturated, cooler than Cultist Purple.

Can I use Marine Blue instead of Cultist Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Marine Blue is noticeably darker, more saturated, cooler than Cultist Purple.

Can I use Cultist Purple instead of Marine Blue?

The same difference applies the other way round: Cultist Purple is noticeably lighter, more muted, 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.