I have some agouti rats but none are agouti selfs. Mine are agouti berkshires but neither of them exhibit the behavior you describe, though my agouti berkshire female, Nutmeg was a very aggressive mother. (instead of sharing babies, she'd fight over them, sometimes harming the babies so severely, I'd have to cull them.)

I am also a believer in personality traits being genetic but I don't necessarily believe it has to do with color. Any rat that bites or is overly aggressive I do not breed more than a few times, and if their offspring are similar, I discontinue breeding those females.