The second ability’s cost reduction can reduce only generic mana in a spell’s total cost. It can’t reduce colored mana requirements.

Ezzaroot Channeler’s second ability counts the total amount of life gained without considering any life you lost during that turn. For example, if you lost 3 life and gained 4 life earlier in the turn, creature spells you cast will cost {4} less.

To determine the total cost of a spell, start with the mana cost or alternative cost you’re paying, add any cost increases, then apply any cost reductions (such as that of Ezzaroot Channeler’s second ability). The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.