Re: Why do some colors get hotter than others when you shine a light on then?

     The explanation is actually fairly straightforward, but you have to 
change the way you think about colors for a moment to understand it. When 
we say something is "white," what do we usually mean? That it is 
reflecting to our eyes evenly all of the wavelengths of light that hit it -
- meaning it's not absorbing much. When we say something is "black," we 
mean just the opposite -- it is absorbing evenly all of the wavelengths 
that hit it and not reflecting much. So that means that if both a black 
surface and a white surface are exposed to the same amount of energy (and 
everything else is basically the same), the black surface will absorb more 
and reflect less, and the white surface will reflect more and absorb less. 
Anytime something absorbs energy, conservation of energy says that it has 
to go somewhere; what's happening with the paper is that the absorbed 
energy is becoming heat. So the black paper becomes hotter than the white 
paper because it is reflecting less energy, and therefore absorbing more. 
Anything that is not white is reflecting more of particular wavelengths -- 
for example, something that appears red is reflecting the wavelengths 
around 7000 angstroms (700 nanometers) and absorbing the others, and so 
on. The other colors will vary depending on what color they are and 
how "deep" the color is, but you can tell which is reflecting the most 
energy the same way -- the other colors will line up from the one 
reflecting the most light (cooler) to the one absorbing the most light 
(warmer), which may not have anything to do with how "dark" the color is 
(green might be cooler than yellow, for example).