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 .” 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.