an FYI about EYE COLORS ... (sorta spoiler)

I hear a lot of talk about the eye color change being complete hogwash and reason enough to suspect the family's deceptive or at least shockingly idiotic. I'm a pharmacist and can say that drops can indeed be put in the eyes to change color to brown.. it's a side effect of medications (prostaglandin analaogs such as latanoprost) used for glaucoma so you have to warn patients about it (also makes your eyelashes longer and darker, something some women use it for against medical advice).

Conveniently for Bourdin's story, the color change is permanent and always goes from whatever lighter color your eyes are to brown, since it's caused by increased pigment production by the iris.

An example (taken from this article about it (http://www.cyberounds.com/cmecontent/art270.html?pf=yes):
http://www.cyberounds.com/assets/05/28/528/figure1.jpg

I doubt Bourdin knew of this phenomenon, but probably just said the first thing that came to mind and it happened to be plausible enough that even an FBI fact check would have to say it checks out...