If you don't control a creature with power 4 or greater as your upkeep begins, Colossal Majesty's ability won't trigger. You can't take any actions during your turn before your upkeep begins.

If you don't control a creature with power 4 or greater as Colossal Majesty's ability resolves, you won't draw a card.

The creature with power 4 or greater that you control as Colossal Majesty's ability resolves doesn't have to be the same creature with power 4 or greater that was under your control as the ability triggered.

You draw only one card, no matter how many creatures with power 4 or greater you control.