Yes, people can have natural yellow eyes. However, yellow eye can also be a sign of illness. So, If you noticed that your eyes turn to yellow, you'd better make an appointment with eye doctor for the sake of your eyes. In common, yellow eyes can be a sign of Jaundice. It is a serious liver diseases. If you have it, you shall treat it immediately.
As far as i know, there is no people with a pure yellow eyes. But there are some people have a complex eye color including yellow. For example, i have saw people who are in yellow eyes with a small bit of blue,red,green on outsides. Some people think it is a mix of hazel with a light and dark color. And the eye color is heredity and determined by iris fibers. And i never see people with a pure yellow eyes naturally.