Well, as a matter of fact, the color of our eyes is decided by the genes which could simply not be change in a natural way. And since this world is very complicated and sometimes miraculous things could happen because the genes and some biological conditions may encounter sudden change which could give rise to a change of the eye color. So, perhaps there are some cases in history. I think it is quite normal.
If you want to have the natural red eyes, you could wear the colored contact lenses which will reach this requirement. You could go to the online stores to choose the red colored contact lenses which will make you look natural. In addition, the red colored contact lenses are so cool which will make you look so fashionable.