Citadel Altdorf Guard Blue Layer Paint is designed for multi-layer application. This dark blue color is slightly transparent so you can use it to build your color over several layers until you're happy with it. Now the paint does require a bit of practice to use, but the results are well worth it.
The layer paints are best used as a 2-step highlight, so two paints for each color but this is a guideline. For example, Altdorf Guard Blue can be combined with Calgar Blue. You start with the darker of the two and apply it to the surfaces that you eventually want to provide this dark blue color.
Because the paint is a bit transparent, you will continue to see the base color a bit, but by using Altdorf Guard Blue together with Calgar Blue, you can use that transparency to apply the layers. If you apply the lightest color after the darkest color in maybe 1 or two layers, the last highlight of the lightest color will ensure that you have a great result.
The color of Citadel Altdorf Guard Blue (22-15) is similar to: The Army Painter Ultramarine Blue (WP1115); Old Citadel Ultramarine Blue; Vallejo Game Color Ultra Navy Blue (72022); Vallejo Model Color Ultramarine (70839); Rackham Wizard Blue 2 (7); Reaper Master Ultramarine Highlight 2 (9189); Coat D'arms Navy Blue (148)