Is there any way to lighten the color of metal posts before situating a new crown?

I would recommend a new abutment (post) made of zirconia. You should have less of a grayness after that. Sometimes the bone and gums of an implant can be thin and you may still have a little grayness. But a zirconia abutment will help a lot!

Hello and thank you for your great question. A lot of patients have the same situation and are not aware of a possibility to make not only crowns out of Zirconia, but also underlying posts (abutments), which hold crowns in place. I had a case some years ago, where patient experience the same problem. After switching abutments to zirconia that problem disappeared.Hope this helps!

Many options. You and your dentist can switch to a porcelain custom abutment post or a Zirconia Bruxzir crown should hide the metal color post as well.  All about having the right dentist and him using the right lab.  Too many dentists out there does not have an artistic eye.