I've actually discovered that if it's loose fitting and there's circulation, dark clothes are better in the heat. Bedouin nomads are known to wear black, loose, flowing robes. The convection properties of dark clothing are mysteriously better (Source). Light clothing also has less UV protection, as it does reflect (but it does not absorb) radiation that gets through. I have not found a study involving skin tight dark clothes and heat dispersal.

That said, I have a white helmet, a Giro Phase. The color probably only matters with something hard like a helmet for how much heat it absorbs, evident of the car test previously mentioned. This could translate to less heat if it's a cool color or white. The inner foam is gray.

Where I live it gets up to 110 degrees with 30-40 percent humidity. I have found putting a wet bandana over my hair helps with cooling, although it hinders circulation. So when the bandana dries out, my head gets hotter.