The Ur-Dragon

Eminence — As long as The Ur-Dragon is in the command zone or on the battlefield, other Dragon spells you cast cost {1} less to cast.
Flying
Whenever one or more Dragons you control attack, draw that many cards, then you may put a permanent card from your hand onto the battlefield.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Sol Ring

Bloom Tender

{T}: For each color among permanents you control, add one mana of that color.