IMO, it can happen. Not sure if they see "color" or just shading, but I'm sure she's just being a picky ball python. I have one that will ONLY eat scented f/t rats, and another that seems to only like mostly white rats. If it's black or another color and not mostly white he'll stck his nose up at it. Not sure if it's imprinting or just coincidence. I suggest sticking to all white rats and not find out lol.