2004-12-01 : Any restrictions on the mana in your mana pool aren’t copied. For example, if you have {C}{W}{W}{B} with no restrictions on it in your mana pool and {U}{U}{U} that can be used only to cast artifact spells, you’ll end up with {C}{C}{W}{W}{W}{W}{B}{B}, {U}{U}{U} that can be used only to cast artifact spells, and {U}{U}{U} that can be used for anything.

2004-12-01 : Doubling Cube’s ability is a mana ability.

2004-12-01 : The “type” of mana is its color, or lack thereof (if the mana is colorless).