Re: how does the sun fade color?

Natalie,

     In the color industry, the term for how much colors fade in the 
sunlight is "lightfastness".  A color is lightfast or light stable if it 
does not fade upon exposure to ultraviolet or visible light.  There is a 
standard scale which rates colors' lightfastness: I="excellent", II="very 
good", III="fair", and IV="poor" (see http://
www.rfpaints.com).  Color 
comes in two physical forms: pigments and dyes.  Dyes are like colored 
salt that are organic molecules.  Pigments come in two forms: inorganic 
(metal oxides) and organic.  Organic dyes and pigments contain chemical 
bonds which can be broken and rearrange if a certain amount of energy is 
added to them.  The sun shines light of various types of energies, 
including higher energy ultraviolet rays which are primarily responsible 
for causing the chemical bonds in some colored molecules to break.  This, 
in turn, alters the shape of these molecules, destroying the parts of the 
molecule that make it colored. So, as more and more molecules are reacting 
with the sunlight, there are less and less still around that have not 
reacted or de-colorized and the overall color seems to "fade" over time...