I suspect that this friend of yours is either pretending one thing but feeling or experiencing something else, or, he is very depressed and negative about something (symbolized by his black skin) (see the meaning of a black man in dreams in visions). It also appears that he needs counseling, that is why he called you by waving at you to go to him (he probably wants to tell you there on the bench what caused him to be depressed and in the bad spiritual situation (condition) that he finds himself in. The black skin does indicate that he was influenced in a bad way with lies or bad messages). The fact that he smiles at you suggests that he favors you, meaning that he has respect for you, trusts you, and also likes you.
For some reason he or she does not know how to approach you for help or something hinders him or her to do so, although he actually wants to ask you to help him.