When Heathcliff is first introduced he is described as a dark skinned boy with dark hair, and because of this people are prejudiced against him. He is called a gypsy numerous times, and the Lintons treat him badly and send him away from their house because of his appearance. Heathcliff also quickly dislikes his son because of his light skin and hair.
Class is also an issue.
There was a class hierarchy in Bronte's England, and this can be seen in the novel as well. The residents of Wuthering Heights seem to be of a lower class than the Lintons at Thrushcross Grange. Even though she loves him, Catherine will not marry Heathcliff after he has been degraded, and instead marries into the rich Linton family, causing all of the major conflict in the novel. The Lintons are of a higher class both because they have more money and don t seem to have to work, and because they are better educated. Catherine tries to better her station both by marrying Edgar Linton and by her constant reading.