Consider the Planeteers for a moment. It’s a multi-racial group of kids serving the greater good; each has a power ring giving them control over an elemental force that when combined creates a guardian of the planet. There were three boys, two girls, with an Asian, a native South American, a black African, and two Caucasian; a more heterogeneous group you are unlikely to find. However, they do raise an interesting question: Is there a reason to include every gender and race in your story just for the sake of inclusiveness?
The problem is that too many people worry about political correctness. There is a fear among far too many writers that by excluding a particular group the writer seems to be racist, sexist, homophobic, whatever. The obvious reaction to this is to create a character that has the appropriate qualities and is likely to relieve the fear of being exclusive. The problem, however, is that the token character is likely to be marginalized, since he or she is there just for the sake of providing a character with the given qualities, and at the very least you are likely to write the character with as little effort as possible.
This means that you have a character that is there for no real purpose, and that is something you should never has as a writer. Every character should fulfill a purpose in the story, be it to drive the story, to serve a symbolic purpose, or even as the expository focus. A character that is there to just have a color may as well be little more than the background, and eventually you will be treating that character precisely as that. Worse, he will act as an anchor on the story and the fans will notice. Worse are those that were drawn to the comic because of that character will get tired of the comic, and will soon start spreading a negative word about the comic, nailing you for precisely the reason that they should.
Now, if you can use the character and turn it around so that the character serves a purpose, go for it. Do not feel as if you need to use the character a particular way; the stereotype is do not have a black person and use that person to inject some level of ghetto or minority issue into the comic. Kwame, the black kid of the Planeteers, was pretty much a waste of flesh because they treated him as the voice of reason, as he was the kid from the wilder regions, so to speak, and then the leader as apparently a way to be different. However, Linka usually gave better advice and Wheeler was the better leader. Kwame would have been the better ecologically-confused kid because he was in a position to least understand worldwide effects. Okay, so I would have liked to have Gi use more brains and Ma-Ti with more passion, but that’s me.
The bottom line is that only include a character is you have an internal reason to have that character around; otherwise cut the waste off before it becomes waste. At the same time, if you do include a character for the purposes of multi-cultural consideration, do not feel obligated to use that character in a stereotypical fashion; feel free to have a black character who is a doctor rather than an ex-street thug. They are your characters; feel free to have some fun with them and use them as they best serve the story, not some idiotic sense of racial guilt that almost always ends up messing things up. Your characters should be guilt free for maximum effect, not minimized to serve some stupid token use.