Over the last couple of years, my roof has been changing colour - looks almost as if somebody has hit it with one of those bombs made of dyed flour 6.png

When I first had the car, I tried to keep it sweet with one of those "restore and protect" kits - Autoglym maybe? Didn't make a lot of difference that I could see...

Anybody got any tips for restoration/upkeep?

Thanks 9.png