Display some line more color

@maki81 really difficult to make out what you are seeing. It might just be better if you take a picture of what your display shows. Post that with your Question Adding images to an existing question

Going by your "description" alone, this sounds like a bad screen. Since iFixit does not yet have a guide for this, use something like this video to work on that. Replacement screens are readily available at many online stores.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!