I have a female rat that hords cheerios and wheat thins. In another rat colony the baby rats will try to eat the same cheerio or wheat thin as an adult, but the baby usually gets it. I've never tried chocolate, I'm not sure it would be good for rodents.
I honestly don't know if the coloring is bad for the snakes. But I have only been giving out M and Ms as treats for not even 2 years and one of the rats that love the m and ms is the longest lived rat I've ever had. I have only had 8 rats as pets in the last 5 years, I usually keep them in groups of 2 or 3 at a time. I got one female as an adult Dec 5 2005, and even though she is failing now, and may not be around in a month, she is at least 26 or 27 months old. The candy hasnt seemed to hurt her, anyway!
Here is a funny story about chocolate and rats. In college I worked in a research lab studying the effects of brain damage and the eating response. Rats with damage to the part of their brain that makes them want to eat stop eating altogether. They would only start eating again when offered one of two things, mother rat's milk and Hersheys milk chocolate. We contacted Hershey to request a list of ingredients so as to find a chemical correlation between the two items. Hershey declined our request based on secrecy issues with regard to their chocolate recipes. That said, I can't look at a Hershey bar and not envision a room full of very patient dexterous people milking mother rats for Hersheys' "secret" ingredient!
Terri