Rule 106.6 · Mana
Some spells or abilities that produce mana restrict how that mana can be spent, have an additional effect that affects the spell or ability that mana is spent on, or create a delayed triggered ability (see rule 603.7a) that triggers when that mana is spent. This doesn’t affect the mana’s type.
Example: A player’s mana pool contains {R}{G} which can be spent only to cast creature spells. That player activates Doubling Cube’s ability, which reads “{3}, {T}: Double the amount of each type of unspent mana you have.” The player’s mana pool now has {R}{R}{G}{G} in it, {R}{G} of which can be spent on anything.
Subrules
Some replacement effects increase the amount of mana produced by a spell or ability. In these cases, any restrictions or additional effects created by the spell or ability will apply to all mana produced. If the spell or ability creates a delayed triggered ability that triggers when the mana is spent, a separate delayed triggered ability is created for each mana produced. If the spell or ability creates a continuous effect or replacement effect if the mana is spent, a separate effect is created once for each mana produced.