Your Wallet, My Profit

Shroud
When this card enters the battlefield, you lose all unspent mana. If you would lose unspent mana,
it becomes colorless instead. You can no longer
tap lands for mana.
When you're opponents tap a land for mana, you
gain twice the amount of mana that land tapped
for.
If you control three or less lands, you can use colorless mana as if it was mana of any color.