ΔE 9.4, close: similar, with a visible difference side by side. Naggaroth Night is a little lighter, warmer than Imperial Blue.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Naggaroth Night is a little lighter, warmer than Imperial Blue.
The same difference applies the other way round: Imperial Blue is a little darker, 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 Imperial Blue on the colour wheel See Naggaroth Night on the colour wheel
All matches: Imperial Blue equivalents · Naggaroth Night equivalents