http://www.silverfallchinchilla.com has a great color section.
Some good questions to ask:
Is there any history of malocclusion in the chin's lines?
Any history of fur chewing?
Does the breeder know the lines and know they're healthy? (For instance I know where every chin back to great grandparents in my breeding chins - where they are, that they're still healthy. A pedigree means nothing if the lines aren't healthy.)
Asking what lines they have never hurts, and asking for references is always a good thing.
Really what I look for is reputation. I know quite a few breeders and private inquiries help me decide what I want. Angela that Chrisanne recommended would be a great start for you.
I also like a breeder to be picky about who they sell to. Myself, I have a detailed questionnaire on my site that anyone interested in a chin MUST fill out before I'll consider selling to them (
http://www.chinnitude.com). I turned away 4-5 people for my last chin I sold - those are my babies and I want them to be taken care of. Keep in mind though, a large rancher will not really be concerned with this - this is where reputation comes in.
Really the best advice I have to offer is read, read, read, read. Research all you can, talk to all you can, and decide if a chin fits your lifestyle and needs in a pet.
