I am not sure how to get the specific color of rats but I do know I switched 27 balls from ASFs to rats cold turkey when I moved across country and the only problem I had was from my problem child Blk Pastel. And she is a problem eater all the time!!
I bred a pretty red eyed siamese to a greyish looking male and get 50/50 babies. Some look like mom and some like dad. And sometime they are curly haired too!!! I have no idea which carries that gene...lol
Best of luck with your pair!