ΔE 22.1, loose: different enough that you should pick on purpose. Imperial Blue is a little lighter, much more saturated, cooler than Dead Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Imperial Blue is a little lighter, much more saturated, cooler than Dead Purple.
The same difference applies the other way round: Dead Purple is a little darker, much 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.
See Dead Purple on the colour wheel See Imperial Blue on the colour wheel
All matches: Dead Purple equivalents · Imperial Blue equivalents