Hanging Gardens of Amonkhet

When Hanging Gardens of Amonkhet enters the battlefield, choose three colors.
{t}: Add {c} to your mana pool. Then put a growth counter on Hanging Gardens of Amonkhet.
{t}: Add one mana of any of the chosen colors to your mana pool. Activate this ability only if there is a growth counter on Hanging Gardens of Amonkhet.