I used to think the same thing but have changed my opinion. As long as the paint on the windows is from one of the PVC paint specific suppliers, there is some good tech in those paints that allow them to reject a majority of the Suns radiant energy.
We have dark painted windows and they don't even get close to the heat of deformation or close to a material in the same color spectrum in another material.
So where does one go to buy paint from "one of the PVC paint specific suppliers"?
The problem the OP faces is that even if this paint guarantees
that it will not raise the temperature of the PVC, if that assurance proves to be worthless and his PVC doors and windows sag and stretch, the only thing the paint manufacturer is on the hook for is refunding his money or providing him with another can of paint, at the paint manufacturer's discretion. So, the OP is risking $15,000 worth of doors and windows, and the paint manufacturer is risking $50 worth of paint. I don't like those numbers.
The paint might work great, as you say, but if I were the OP, I'd only paint one window until I had sufficient confidence in the paint to go forward with the other doors and windows.
Or, just play it safe and leave the doors and windows unpainted.