ΔE 25.3, loose: different enough that you should pick on purpose. Imperial Purple is noticeably lighter, more saturated, warmer than Marine Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Imperial Purple is noticeably lighter, more saturated, warmer than Marine Blue.
The same difference applies the other way round: Marine Blue is noticeably darker, more muted, 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.
See Marine Blue on the colour wheel See Imperial Purple on the colour wheel
All matches: Marine Blue equivalents · Imperial Purple equivalents