I’m currently trying to make a UGC Headphone Concept for a group that asked me for it. Anyways I made one side of the Headphones, duplicated them, made it at the right side of the model and joined/grouped them.
After doing that I did some texture work but now their are some weird color differences. Under here are some screenshots.
This is usually due to unwanted topology. Try going into face select mode and edit mode and select all faces and hit xray mode to see if there are any unwanted faces. If so, delete them.