It's happened, the very thing I was afraid of...

I caught the breeding bug.

The only problem is that I don't remember much of anything about genetics from the little I learned in my bio class. I know how to do punnet squares. I under stand about dominant and reccessive traits, but I'm still a bit confused about co-dom traits. What is the difference between dominant and co-dom? Is it possible to have co-dom hets?