Citadel Kantor Blue Base paint is designed to give a smooth, solid dark blue color over an undercoat and for that reason this will almost always be the first paint you use on a miniature. Shake the dark blue paint before using (you can make this easier by adding an agitator ball).
The dark blue paint can be a bit thick sometimes and then you just add a few drops of water to your pallet. You really don't need a lot of water. Something to watch out for is to make sure you don't apply too much paint so that you don't start to hide details.
Another important functionality of this dark blue paint is that it not only covers the undercoat, but also covers other colors. So if you later miss something about this color, you can easily paint over it with this Kantor Blue base paint.
The color of Citadel Kantor Blue (21-07) is similar to: The Army Painter Deep Blue (WP1116); Old Citadel Regal Blue; Vallejo Game Color Imperial Blue (72020); Vallejo Model Color Dark Prussian blue; Instar Marianas Blue; Reaper Master Brilliant Blue (9116); Coat D'arms Royal Blue (110).