Chickens can eat potato peels, even the ones turning slightly green. Yes, the green ones can be toxic, but only in very large quantities. If chickens are getting the bulk of their diet from laying hen pellets, then they won't overeat on the questionable items. However, you don't want to feed them quantities of food that they can't or won't finish, and that will make a mess of your yard (that's why I have a compost pile in my chicken run. They shred what they don't eat. They'll be fussy if they have a choice. For example, there's no harm from putting coffee grounds in the compost that your chickens have access to. However, that certainly wouldn't be a healthy food for them it that's all they got! See my compost system here: http://hencam.com/compost-in-the-chicken-run/) It's much worse to give them lots of bread and cracked corn which will make them fat and upset their mineral balance than to give them access to a compost pile that has lots of variety.
The only absolutely toxic in any quantity item that I know of is avocado.
I have a feeding FAQ here:
In your situation, I'd just give them the laying hen pellets. If you want to give them a treat, they'll be very happy to see a tomato or a watermelon rind!