Reaper
HD Solid Blue is a very deep blue. I use it for librarians and it looks amazing. I can post a pic after work today.
Edit for pics. Primaris Librarian is Solid Blue with Nuln Oil and I believe Army Painter Ultramarine Blue edge highlight. Space Hulk Librarian is currently just Solid Blue basecoat.
Dang I'd forgotten just how awesome that Primaris Librarian turned out

That may have been two coats of Nuln Oil--I don't remember for sure. Now I want to go back and deepen the shade and highlight those yellow tubes a bit--they look a bit flat!