Morocco, from both his name and his self-description, appears to have darker skin. He appears to consider his appearance a deficit in wooing Portia that he needs to address, despite the fact that the choice of a casket, not Portia's opinion, is what will determine who becomes her husband.
Morocco seeks to assert his humanity by saying that an incision would show his blood is as red as the lightest-skinned person from the far north. He also states that his appearance intimidates other men, implying that it is a sign of masculinity and that beautiful young women in his own country find him handsome. He ends by saying that he is proud of his skin color and would not change it, except to sway Portia's heart in his favor.
We learn from this that Morocco is well aware of European racism and hopes to address this elephant in the room rather than pretend it does not exist. He reveals that he is a smooth-talking, diplomatic person who tries to disarm opponents by naming problems before they do. While he has his deeper problems as a candidate for Portia's hand, we can appreciate that he wants to win her heart even though he doesn't need to. It seems important to him that he not only get Portia through the terms of her will but that she sees him as a man of value.