Subject: How does guage symmetry work?

I am currently reading a book on quantum physics, and I've reached a part on 
guage symmetry. I'm a little confused by what was said, so I thought perhaps 
you could enlighten me. Basically, I understood that each of the four forces in 
nature are an outgrowth of the symmetry that nature likes to conserve within 
herself. That is, emphasized by the general theory of relativity, the force of 
gravity exists because an accelerating object could justifiably be deemed as 
standing still if we incorporate a gravitational feild into our interpretation. 
The book went on to point out how the strong force exists because of how the 
red, blue, and green charges of quarks could be considered to be shifted to 
yellow, indigo and violet, and the behavior observed by them would be 
unchanged. For one thing, I don't understand what a yellow, indigo and violet 
shift would mean (do those charges even exist?). But more pressing for me is 
that it seems that the behavior of quarks is due to their attractive and 
repulsive charges TO BEGIN WITH, and that it is not an OUTGROWTH of their 
symmetrical property. In other words, I don't understand how the strong force 
follows from this type of symmetry. Since this symmetry is said to apply to all 
the forces, perhaps in your response you could provide an example using the 
electromagnetic force instead seeing as how I am much more familiar with 
protons and electrons than I am with quarks. Thank you.

Re: How does guage symmetry work?