When Plaza of Harmony enters, if you control two or more Gates, you gain 3 life. {T}: Add {C}. {T}: Add one mana of any type that a Gate you control could produce.
2019-01-25
Any additions to a Gate's land types or abilities gained by a Gate can affect the types of mana a Gate can produce.
2019-01-25
Plaza of Harmony checks the effects of all mana-producing abilities of Gates you control, but it doesn't check their costs or legality. For example, it doesn't check whether a Gate is untapped.
2019-01-25
The types of mana are white, blue, black, red, green, and colorless.