But where do I find my petz' eye color in their .pet file? 

Oh dear... the eye colour is under the [Ballz Info] section, and it is actually an outline colour. Possibly the best way to find it, for most pets, in the hex editor is to find [Ballz Info] and then look down until you find the number 244 directly after an instance of hexadecimal 0A. This is the actual "pupil", which is why in most petz it's 244. The outline colour number comes next and is the iris. Of course, if you have a pet which is 244-black all over (such as my Dark Cat), or the pupil isn't black, then you're going to have to either count your way down the 0A bytes until you reach the correct number for the iris or you may want to use my "wordpad" method (which I'm not going into here, I've written all about it elsewhere in my tutorials).