Personally I think it's hideous. Your hair should never be lighter than your skin. That's just horribly wrong. In fact the very first question I ever asked on this site when I opened my account 3 years ago was this exact question lol.
I don't think it looks that bad on some people, and I definitely don't think it looks unclean. It is a little unnatural looking. I like Rihanna's red hair, and I don't think the girl in the 4th picture looks that weird.