ΔE 9.1, close: similar, with a visible difference side by side. Imperial Blue is a little lighter, more muted than Sapphire Blue.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Imperial Blue is a little lighter, more muted than Sapphire Blue.
The same difference applies the other way round: Sapphire Blue is a little darker, 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 Sapphire Blue on the colour wheel See Imperial Blue on the colour wheel
All matches: Sapphire Blue equivalents · Imperial Blue equivalents