Thinking about doing the white roof on my black truck. Definitely could use a little help reducing cabin temps this summer. Already touching 100? here and will be so for the next five months. ('?' = ALT+248 on the 10-key pad, by the way.) Also considering that 1500? exhaust paint in a bright silver. It's got ceramic in it, which I suspect might further insulate the sheetmetal.

The experiment:
Pick up a meat thermometer at the local grocery store or whatever a week before you plan to paint the roof. The cheap kind with the dial. Park the truck like usual (windows up/down, sun shade, whatever) and leave the thermometer on the driver's seat. Jot the time and temp down when you get in. After the paint job, repeat the process. See what - if any - difference it makes.

I've always got a meat thermometer in my truck. It's a throwback from my old Galant VR4. I used it to confirm my AC was working at its best. Stuck in traffic in 110? heat, that car would push 45? air through the dash vents. It was glorious.