Blue may be the main color that is required. Aside from the namesake card there's probably the most cards in blue that change lands to its way of life. These include, but isn't limited to,
Aquitect's Will
,
Lingering Mirage
,
Sea's Claim
, and
Spreading Seas
. Various cards can also change things to any type or only until end of turn, to include
Convincing Mirage
and
Shimmering Mirage
respectively. The former is preferred since it's permanent.
Blue also has the ability to change the land type on a card's text box. These include
Crystal Spray
,
Magical Hack
,
Mind Bend
,
Spectral Shift
,
Trait Doctoring
, and
Whim of Volrath
. While some of these only last until the end of the turn, they both have a number of uses. First, all but one of these can go onto
Isochron Scepter
which can then be used multiple times each round, if untapped. Second, the temporary ones can be used to change the Fountain so that it gives specific people specific land types. On top of that, the permanent effects can simply 'color shift' the Fountain to give everyone the same type that they can't use. Watch out for stray
Urborg, Tomb of Yawgmoth
's though!
I'm also interested in the idea of putting a
Clever Impersonator
on a
Soul Foundry
or the like and making it copies of either Fountain or one of the aforementioned land-changing enchantments, or some cards that will be mentioned later.
If every land eventually becomes the same type then we'll need a way to stop our Fountain from removing flood counters. The easiest and safest way would be to bounce our fountain, and blue is the best at doing this.
Another way we can ensure the Fountain continues to flow is with various effects that remove counters, such as
Chisei, Heart of Oceans
or
Power Conduit
. The latter can work with a large number of cards for the +1/+1 / charge counters depending on the direction the deck goes.