Channeled Dragonfire

Tapping a creature won’t reduce colored mana components of harmonize costs.

To determine the total cost of a spell, start with the mana cost or alternative cost (such as a harmonize cost) you’re paying, add any cost increases, then apply any cost reductions (such as the cost reduction from tapping a creature). The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.

A spell cast using harmonize will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.