This thread is interesting.
https://www.filmjackets.com/forum/viewtopic.php?t=2624 Some using Lemon juice and sitting it in the sun for a while. I know for a fact that it works on hair, so could work on cloth also. You have to be in the sun for it to work. The acid in the lemon reacts with the sun and brightens it. Also, wouldn't washing the whole jacket fade the darker blue, lighter each wash, could be worth a shot. Just keep washing until the blue got to the desired colour. Don't know if this would effect the grey areas also though?!