I can only answer if it were me and my snakes: I would not feed infested rodents to my snakes. Just me.
I'd think that if your snake is 2 pounds (=a bit over 900g) then feeding a 90-100g rat every 7 days should be fine.
I *think* that the yellow is the keratin in their hair. I am not certain as this info comes from my high school son who is of the impression that he knows all that I don't (...may I live through this stage!!)