Beauty is in the eye of the beholder and only goes skin deep. Nonetheless, different societies have different standards of beauty. For instance in Iran the perfect nose is an ideal one, in parts of Africa fat is considered pleasing to the eye. However for some beauty becomes an obsession! Americans obsess over being thin and "perfect" through having multiple plastic surgeries.
Pecola and the Breedloves see themselves as ugly because they have dark-skin and "nappy" hair. As a result of their low self image they are perceived as ugly by others. As the story progresses Pecola becomes intrigued by Maureen Peel a pretty "high-yellow girl" that everyone from teachers to the boys are smitten by. In the book, Pecola and others place a high emphasis and praise on having fair skin.
Self image is a very strong factor in others perception of beauty. Although society places high standards on image/beauty its important to know who you are and to stay true to your self at all times.