The name says it all But apart from Space Marines, this is also the perfect colour for Lizardmen, Imp. guard, Cygnar or American Civil War for
Colour Primer: Ultramarine Blue
Getting more used to the contrast paints, using army painter spray ultramarine blue as a base, then Tamiya spray white for cover, and a tamiya flat white for highlights. : r/Warhammer40k
Alternatives to Ultramarine Blue: Army Painter Primer?
The Army Painter - Colour Primer - Ultramarine Blue
The Army Painter Warpaint Air Ultramarine Blue - Acrylic Non-Toxic Heavily Pigmented Water Based Paint for Tabletop Roleplaying, Boardgames, and Wargames Miniature Model Painting : Arts, Crafts & Sewing
Colour Primer Sprays, Priming of models & terrain
Army Painter: Spray: Ultramarine Blue
The Army Painter Warpaint Air Ultramarine Blue - Acrylic Non-Toxic Heavily Pigmented Water Based Paint for Tabletop Roleplaying, Boardgames, and Wargames Miniature Model Painting : Arts, Crafts & Sewing
Armada Games - Army Painter Ultramarine Blue Paint