I think it is very important to realise the historical context of the time regarding issues of skin colour. We are so exposed to a variety of different skin tones today that we hardly think of it as anything strange, and if there is anyone who does, we label them a racist, with good reason. However, in Shakespeare's times, only a minority of white English people would have seen a black person, and so there was an aura of mystique and wonder about them. Many people actually believed, for example, that if you gave a black person a good bath and scrub, they would come out white. Therefore it is important not to jump to conclusions and label Portia as a racist. Morocco is trying to present himself as a fellow human being to Portia, who probably would not have travelled that much and may have been scared or nervous about meeting someone like Morocco for the first time.