Trading iPhone 11 for different color

You have 14 days to return you iPhone without penalty.

Yes, almost certainly.

Return to the place you purchased it.

You would have to return it for a refund and buy the new phone if they have it in stock.

You can exchange your phone without a restocking fee but it has to be within 14 days of purchase.

If you did not purchase at an Apple Store, then you need to check on their return policy.