So, I attmepted part one of my experiment today,

Fail. The weather was all over the place sunny, rainy, sunny, rainy.

But, when it was sunny it was easy to tell, just by feeling, that some of the colours were absorbing the heat a lot faster than the others.

I've also had an idea: When I heat up the steel next time, I will time how long it takes for each colour to return to orginal temperature. Hopefully this will eliminate this problem.