Well, it is because that purple eyes are real. She has an extremely rare condition called Alexandra Genisis causing as humans to have completely pitch white skin with purple eyes but for Jeanette as a chipmunk they have brown fur with a very pale yellow patch on her belly and chest kind of like a grizzly bear and of course purple eyes. Which brings me onto my question is that why does no one point out colours of either signature colours or eye colours whether any chipmunk are wearing lenses to match their eye colour to their signature colour. If so then... wow.
You know, whenever Jeanette had her glasses taken off, she should've had those simple black dots for her eyes, you know, to look like some characters like Chuckie from Rugrats and Phoebe from Hey Arnold whenever they have their glasses taken off, for instance.
You might think it doesn't exist because it has only ever effected about 60 people in history of humans. This condition was named after Alexandra who had bizzarely pale skin and her retinas looked rather purple and this was hundreds of years ago I don't know the date. Science believe that it might be a faulty gene or a disease that they cannot explain such as the water disease that has only affected 28 people.