That Glossy Sea Blue really is very dark and black looking in some lights
These things have been sitting there for years baking in the sun, and I am sure has faded a bit, but even then is still quite dark
The Vallejo Glossy Sea Blue over a light grey or white base I think is a great choice
Tamiya XF-17 is also a good choice if you prefer Tamiya, put I like to add a little bit of a bright blue/light grey to the Tamiya paint for highlights
these two were done with the Vallejo Model Air Glossy Sea Blue straight from the bottle, then given a very light sludge style panel washing with some light grey, almost white, oil paints for some tonal variations
and to demonstrate the way the paint shifts from blue to black depending on lighting, this is with a cool white light, it looks more blue
and a warm white, looks much more black