Any tips for avoiding the gray form when making chicken stock? If not, any tips on getting rid of it?

Just a tip for skimming the foam off: I bought one of those fine mesh skimmers at an Asian market for probably a dollar or two. It does the trick very well. Usually I hold the pot lid with the inside up next to the pot and as I skim the foam, just put it on the upturned pot lid. After I've skimmed most of the foam, I dump what's on the lid and then usually get a little more foam off after that.

I would turn the heat down so it's at a simmer, rather than a boil, that will help. Also, if you do see gray foam, just skim it off the top.

You really can't avoid it: the scum is coagulated proteins in the meat and bones that form as the water heats and rise to the top. Just skim it off and carry on--almost all of it is produced in the first 10 minutes or so after the stock reaches a simmer.

First, don't boil it. Let it come to a stage where you just begin to see bubbles. Skim off that foam as it comes up. You can make a decent chicken stock in 3 to 4 hours. After that pour it through a fine mesh strainer lined with cheese cloth. And after that refrigerate overnight and in the morning take off the "fat cap" which will have formed. Underneath that you will have what looks like jello but is really a nice clear stock when heated.