I bought shingles from Lowe's and had them delivered. The roofers came and installed. The shingles are mixed matched. I have two different colors. Who do I call to get this fixed.

Do u have documentation on what u ordered &what was to be delivered, through Lowes or contractor to track mistake

This is a real humdinger. First off. The roofers should not have installed it. They should have recognised the situation and consulted you and the crew leader/bossman. Was the roof installed through Lowe's? If so contact the Install sales department. They will be willing to get the ball rolling to get the issue worked out. If it was installed through another contractor. That is their fault. And Lowe's is not responsible. If the product was delivered but not installed there would be no issue with returning the wrong shingles.

Contractor or call lowes corporate.

I would ask to see if your roofing contractor has a good relationship with Lowe's first to see if they could come up with some kind of solution to resolve the issue. But, but Lowe's will be the one to pay your roofing contractor to tear off and put the correct ones on since it was their mistake. If you would have let the contractor buy the shingles it would have been on them as well. But before you do anything say a good prayer to the Lord he'll help. He's first in everything you do!!!