The aerohead is hot AF at least my black one was... Maybe the lighters colors don't get as hot but ventilation is pretty poor. Also, and this might be an issue if humidity is high or raining, it's almost impossible to keep the visor from fogging. I did two 70.3s with it and the first one was downright dangerous where I could barely see the road for the first hour or so and then I had to continuously wipe the visor to see where I'm going. The second race I used a defogging solution, worked marginally better but still had to wipe the visor all the time.
This helmet might be fast and look cool if you're sitting in a wind tunnel but if you crash into a pole or have to mess with the visor every 5 minutes then I'm pretty sure you lose more than 5W.
Color is not going to make a difference. It is a big chunk of foam, like a Styrofoam cooler. the higher surface temperature of a darker color is not going to conduct through the foam to the inside. Not to mention that the surface is going to have constant airflow over it, to it is not going to heat much more than the lighter color, compared to if both helmets were stationary.
I am waiting for someone to claim that darker helmets are faster. Darker helmets heat up the air. Heated air is less dense. Less dense air means less drag.