ΔE 7.0, close: similar, with a visible difference side by side. Blue Ink is more muted, cooler than Imperial Navy. They are different kinds of paint: Army Painter Imperial Navy is an opaque base/layer paint and Reaper Blue Ink is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Blue Ink is more muted, cooler than Imperial Navy. They are different kinds of paint.
The same difference applies the other way round: Imperial Navy is 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 Imperial Navy on the colour wheel See Blue Ink on the colour wheel
All matches: Imperial Navy equivalents · Blue Ink equivalents