Citadel Caliban Green Base paint is designed to give a smooth, solid dark green color over an undercoat and for that reason this will almost always be the first paint you use on a miniature. Shake the dark green paint before using (you can make this easier by adding an agitator ball).
The dark green 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 dark green 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 Caliban Green base paint.
The color of Citadel Caliban Green (21-12) is similar to: The Army Painter Angel Green (WP1112); Old Citadel Dark Angels Green; Vallejo Game Color Dark Green (72028); Vallejo Model Color Deep Green (70970); Instar Military Green; Rackham Diisha Green (18); Reaper Master Pine Green 2 (9010); Privateer Press P3 Gnarls Green 2; Coat D'arms Dark Elf Green (111).