Citadel Caledor Sky Base paint is designed to give a smooth, solid blue color over an undercoat and for that reason this will almost always be the first paint you use on a miniature. Shake the blue paint before using (you can make this easier by adding an agitator ball).
The blue paint can be a bit thick sometimes and then you just add a few drops of water on 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 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 Caledor Sky base paint.
The color of Citadel Caledor Sky (21-09) is similar to: The Army Painter Crystal Blue; Old Citadel Enchanted Blue; Vallejo Game Color Magic Blue (72021); Vallejo Model Color Dark Blue (70930); Instar Sapphire Blue; Rackham Ephren Blue (4); Reaper Master Cyan Blue 2 (9117); Privateer Press P3 Cygnar Blue Highlight; Coat D'arms Wizard Blue (114).