Historical Rules · 5 February 2021
Rule 106.5
Official source text from the 5 February 2021 Rules release
If an ability would produce one or more mana of an undefined type, it produces no mana instead. Example: Meteor Crater has the ability “{T}: Choose a color of a permanent you control. Add one mana of that color.” If you control no colored permanents, activating Meteor Crater’s mana ability produces no mana.