What would casting a card with Sunburst do with an effect like Jodah's?
You would get 5 counters.

The reminder text and the comprehensive rules for Sunburst say “for each color of mana spent to cast it.” So all that matters is how many colors you spent to cast it; not what the casting cost is or anything like that. 


  702.43a Sunburst is a static ability that functions as an object is entering the battlefield from the stack. “Sunburst” means “If this object is entering the battlefield from the stack as a creature, it enters the battlefield with a +1/+1 counter on it for each color of mana spent to cast it. If this object is entering the battlefield from the stack and isn’t entering the battlefield as a creature, it enters the battlefield with a charge counter on it for each color of mana spent to cast it.”