well i think it is both ways...opposite attracts in some respect and homogamy also attracts as well.i will like to think that homogamy is the primary determinant of acceptance in any relationship. you have to be similar at first to a person before the idea of having a relationship pop up.such similarity may be in colour,religion,tribe, social class etc...the list may be endless. after this comes the secondary determinant which is the difference which will complement the couple...i think a balance between this 2 large force may be responsible for attraction