I feel like the creature token ought to be a Pegasus Unicorn Pony. Earth ponies have their own special attributes (greater physical strength, connection with plants and animals) that the other types don't share, but the alicorns do share them.
"1, T: Destroy target creature that shares a color with mana spent to activate this ability. Put an element counter on Elements of Harmony. Spend only colored mana to activate this ability. 1, T, Remove six element counters from Elements of Harmony and sacrifice it: Put a colorless 6/6 Pegasus Unicorn creature token with "T: Destroy target colored creature." onto the battlefield."
Repeatable destruction for colorless with a game-changing final effect? That is powerful. I'd change the cost of the first ability to 2T, remove the no colorless restriction and say that you could only destroy a creature which shares a color with mana used to activate the ability. Second ability could be a tap-sac.
Again, I feel the need to fix the wording on this, otherwise it doesn't work. The first ability should not read "Destroy target creature THAT shares a colour...", but "Destroy target creature IF IT shares a colour...". The reason is the targets are chosen before costs are paid. When you choose a target for the ability, you haven't yet paid the mana, and thus the game doesn't even know what you're allowed to target.