Reflecting Pool‘s ability allows it to produce any one mana of a type that another land that you control could produce. First of all, in order for this ability to produce any mana you must control at least one other land that is capable or producing mana. Controlling just another Reflecting Pool will not work, as each of these two Pools will ‘look’ at the other and see that each cannot produce mana.

There are currently only six types of mana; white, blue, black, red, green and colorless. Any restrictions on what mana can be spent on are not part of its type, so the mana generated by Reflecting Pool will not copy those restrictions. An example of a mana ability that produces mana with a restriction would be Ancient Ziggurat ability.

Additionally you do not consider the costs necessary to pay a mana ability to determine what it is capable of producing. For example, Reflecting Pool will be able to generate mana of any color even if the only other land controlled by this player is a Vivid Creek with no charge counters on it.

Finally, you do factor in type changing effects and replacement effects when determine what type of mana a land can produce. A Forest that has been enchanted by Spreading Seas will generate blue mana, not green. Reflecting Pool’s ability will therefore only be able to generate blue mana in this example.

In other words, if you were to activate a mana ability of a land you control the type of mana that could be produced is what Reflecting Pool can produce.