ΔE 17.7, loose: different enough that you should pick on purpose. Imperial Blue is noticeably darker, more muted, cooler than Ghost Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Imperial Blue is noticeably darker, more muted, cooler than Ghost Blue.
The same difference applies the other way round: Ghost Blue is noticeably lighter, more saturated, 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 Ghost Blue on the colour wheel See Imperial Blue on the colour wheel
All matches: Ghost Blue equivalents · Imperial Blue equivalents