Pause for Reflection

When calculating a spell's total cost, include any alternative costs, additional costs, or anything else that increases or reduces the cost to cast the spell. Convoke applies after the total cost is calculated. Convoke doesn't change a spell's mana cost or mana value.

Tapping a multicolored creature using convoke will pay for 1 generic mana or one mana of your choice of any of that creature's colors.

Because convoke isn't an alternative cost, it can be used in conjunction with alternative costs.