Write what you know. Writing white people with gender issues will come off better than pretending you can understand a minority character just to stick them in. Usually when writers force minority characters in they either accidentally become racial stereotypes, or they just end up written like a white person with brown skin. If a good minority character comes to you that isn't a gimmick, by all means go for it, but most people would rather see a bunch of white people well written than feeling like minority characters are being forced on them.
Also you said in your story there's a REASON they're white mostly, and that's better than most stories. Most of the time they're just white people because that's all the author can come up with. So kudos.