ΔE 16.9, loose: different enough that you should pick on purpose. Imperial Blue is a little darker, much more muted than Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Imperial Blue is a little darker, much more muted than Blue.
The same difference applies the other way round: Blue is a little lighter, much more saturated.
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 Blue on the colour wheel See Imperial Blue on the colour wheel
All matches: Blue equivalents · Imperial Blue equivalents