I suspect that the reason my wife doesn't like my son's girlfriend is due to racism but she denies it since we are an interracial couple. I need advice on how to address this with her.

My wife is black. I am white. Our kids are mixed and all 3 are teenagers. Our son is our middle child and is currently dating a white girl. I don't know what dating entails anymore. They rarely even get together but he told us he had a girlfriend and she has come over a few times.My wife doesn't like our son's girlfriend for no real reason that I can tell. Our son is highly motivated and determined. He loaded up on AP classes, plays numerous varsity sports, and is reaching high for college. You might think that's why my wife is upset about him dating, but she was excited when he first started talking about his girlfriend and she's just as determined as our son both academically and athletically. She didn't have a problem with our son's girlfriend until she met her and she asked our son why he didn't mention that she was white. My son said he didn't think it would matter. I agreed with him. My wife says that he was hiding it for a reason.Anyway, my son can sense that his mom doesn't like his girlfriend and I am afraid that he's going to start pushing us away. I have tried talking to my wife about It but she denies it has anything to do with race because we are an interracial couple but to me that sounds like "I can't be racist because I have black friends" kind of reasoning. via /r/Parenting http://bit.ly/2WlmUnD