Throne of Eldraine's chosen color is not "Blue" available.
Steps
If able, activate
Throne of Eldraine's first ability by tapping it, adding ({U} magic symbol) ({U} magic symbol) ({U} magic symbol) ({U} magic symbol) that can only be spent to cast blue monocolored spells.
Cast
Whim of Volrath with buyback by paying ({2} magic symbol) ({U} magic symbol) , targeting
Throne of Eldraine.
Orvar's first ability triggers, creating a copy of
Throne of Eldraine. Choose "Blue" as its color as it enters the battlefield.
Resolve
Whim of Volrath, changing nothing and returning it to your hand.
Repeat.
Notes
Once you have infinite mana to cast
Whim of Volrath, you can either name different colors, draw cards instead, and/or target other permanents.
Results
Infinite ETB.
Infinite storm count.
Infinite creature tokens.
Infinite magecraft triggers.
Infinite landfall triggers.
Infinite copies of permanents you control.
Infinite colored mana that can only be spent to cast monocolored spells.