There are many subtle ways to introduce the idea. Why not watch some good amateur interracial porn with her. Let her see the white wives beam with pleasure during and after. Then..........you should say nothing after the first 2 or 3 movies, just watch with her. Let her watch without any coaxing from you at first. After watching 3 or 4 movies (or more) within a span of one week or 2, you just bring up how well the women in the movies enjoy it. Then you introduce the idea as best you can. You know your wife, we dont, so you know the best way to introduce it. The idea I'm getting at is............you cant just show her one movie and be all over her trying to get her to accept the idea. Go slow, and you will have better results.