Does Rule 103.3.a.1 mean that if your chosen champion is "Garen, Commander" and your legend is "Might of Demacia", you can only have yellow runes in your deck?

Ruling: No, this is a typo in the rules. The rule should reference your "legend" rather than your champion when determining which runes you can include in your deck.

Nuances:

• This typo has been reported as feedback and will be corrected in the next version of the rules