Go sleeveless in the summer. That helps a lot more than color choice.
I'm curious about the color in relation to heat. What's the actual science. I feel some of it is just centuries-old wives tale.
the science is the lighter the color of something, the more light waves are reflected off of it rather than absorbed. that is why DDs catching helmet and chest protector are white primarily.
that being said, fabric and cut can make a huge difference as well. if I had my way, DDs team would wear orange or gray as primary colors (navy is their other color) in hot weather. but it appears they will have navy jersye with orange pants, and orange jersey with navy pants.