You know, when you look at it in a neat little list like that it makes it apparently obvious that Blue/Water Mana is quite shorted.
Every color gets 4 kingdoms dedicated to their Mastery except Blue, having half as many.
With enough room left on the map for 11 more kingdoms, 3 of those will have to be dedicated to Blue to nearly even them out. With 3 different Masteries getting a slight edge.
EDIT: Whoops, noticed Brown's count as well. In which case only 1 Mastery would get the special privileges of a 6th Kingdom. (If, of course, two of the apparent kingdom slots don't get meshed into one. Like the places to the right of Grosh-Nak/Forest of Thorns could be, for example.)