On a scientific and genetic level it is actually possible. You are making the assumption that the protein chain that effects the pattern of a "morph" will never have an effect on any other functions of the animal's development. Just because a genetic mutation effects the pattern or color of an animal does not automatically mean it stops there. It could also effect the animal on a neurological level or in a multitude of other ways. Just because it isn't always the case, doesn't mean it is never the case. That being said, it is possible that a visual morph can also carry a secondary issue, and the expression or severity of that issue may vary.