I am not kidding, its the real deal, My company has spent a lot of money and time on R&D to formulate plastic that is UV stabilised to try and slow the UV deteriation process down,eliminate it we can not!
I manufacture shopping trolleys, they all have plastic components and spend a lot of time in the sun, eventually the colour is stripped from the plastic leaving it in its natural state if not adequately UV treated (which is expensive), Tanks are not UV stabilised as far as I know especialy not vintage ones.