Today I wore my white Cyclechat jersey for the first time out in the sun and within a couple of miles I was cooking, the side of my body facing the sun was toasting, usually I wear Reds, Blues and Black and I've never felt the heat like I did today. I've always gone along with the theory that whites cooler in the sun, but today has proved me wrong and won't make the mistake again.
But on the other hand, it is a good snug fit and also its white inside, so perhaps the heat transfer from the body is not so good and also if it was a very loose fit then heat from the outside may not transfer so easily to the body.