406.7.

Some abilities produce mana based on the type of mana another permanent or permanents could produce. The type of mana a permanent "could produce" at any time includes any type of mana that an ability of that permanent would generate if the ability were to resolve at that time, taking into account any applicable replacement effects in any possible order. Ignore whether any costs of the ability couldn't be paid. If that permanent wouldn't produce any mana under these conditions, or no type of mana can be defined this way, there's no type of mana it could produce.

Example: Exotic Orchard has the ability "{T}: Add to your mana pool one mana of any color that a land an opponent controls could produce." If your opponent controls no lands, playing Exotic Orchard's mana ability will produce no mana. The same is true if you and your opponent each control no lands other than Exotic Orchards. However, if you control a Forest and an Exotic Orchard, and your opponent controls an Exotic Orchard, then each Exotic Orchard could produce {G}.