Dark tooth under crown showing through - best option? (Photos)

I had a root canal done about a year ago under a crowned front tooth. The underlying tooth began darkening and showing through. I had it internally bleache twice but continued to darken. I went to a cosmetic dentist who replaced the crown and tried to mask the underlying tooth. He replaced the crown but the gum line is still dark. So after spending 1000’s of dollars on a new crown I am back to square 1. I am very disappointed and trying to figure out what to do next.