I read the entire first and last pages of this thread, but not the middle ones, so...
My wife and I have identical M7's, purchased in May 2013. Both cameras have operated fine, until about a month ago, when my wife complained that hers was taking really lousy pictures. I know she was happy with her camera, before, so what happened? When I went to look at her phone, it was exactly as the others described: purple/pink tint, very grainy in low-light situations. She is not so great at updating her software, so I spent several hours, making sure she had the latest updates, including the monstrous one from ATT that came out in about June. Clearly, her camera has gone bad, and it wasn't the result of any software updates.
When I called HTC, the person walked me through a few steps, then said, yep, it's bad. The only thing to do was send it in for repair, which would be between $200 and $250! For an 18-month-old phone? No, thanks. Very disappointing, as we really love everything else about our One's.
Not sure what steps to take next, and if it's a new phone, not sure of brand.