Mana produced by Cultivator Drone may be used to cast any colorless spell, including most artifact spells, face-down spells, and spells with devoid.

Some triggered abilities include a cost as part of their resolution. For example, Bearer of Silence’s ability says, in part, “When you cast Bearer of Silence, you may pay {1}{C}.” You may use mana produced by Cultivator Drone to help pay that cost. In fact, you could tap two Cultivator Drones to pay the entire cost.