White and Ground should be immutable. Was this prewired for a fan? find which of the black or red is controlled by the switch you want to use and that goes to the black on the light.

It sounds like they used 14/3 or 12/3 wire so they could control the fan and light separately, which is very common in newer installations. You need to use either the black or the red wire at the fixture (whichever one is currently connected to the wall switch), and leave the other wire disconnected and capped at both ends. Then connect white to white at the fixture and connect the ground to the fixture body or ground wire on the fixture.

Bruce