I'm trying to find a book which I used to read at university some years ago. I remember just some very scarce details. It was English or American SF about aliens who invaded and occupied the Earth. Human race was used by them as slaves. In the beginning of the book the story focuses on an alien girl who thought about human appearance and position in their some kind of society. Unlike humans aliens had clouds instead of hair. It would be very cool if you are able to help me.