Is this hair miniaturization or turning white/grey? (Photo)

This needs an in-person evaluation. I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

Miniturization is a process where a large, healthy, "terminal" hair fiber becomes narrower, shallower, and may have a loss of pigment. This very well may be miniturization.  As you have had hair loss for many years, I hope that you have someone you trust guiding your treatment to keep your hair as healthy and dense as possible. Best of luck. 

We don't diagnose miniaturization based on one hair. The only thing that can be said is that one hair is thinner than the other. Miniaturization is a field phenomenon whereby many hairs in a defined area become thinner. It is normal for a few hairs on anyone's scalp to be thinner. The rest of your questions really require an in person exam.