If you want your wife to get some new cock than she has to make the decisions. If she wants white than that's what she should have. Why would you even consider trying to talk her into anything else? It isn't you, it's her. Yeah, you want to see it but the work is being done by her. She will more that see it. If you want to see it again, don't push her in a different direction. She may never go black and that is her choice. If you don't like that idea than maybe best to put a stop to all it right now.
I know these activities like to show the taboo white girl with the big shafted black man. Reality is that there are probably a lot more white women that are screwing white men that are not their husbands. Oh, and all black men do not have dragging cocks. I have met both black and white that didn't even reach past my little hands. A few inches. It's just the taboo aspect of it even though society is changing and their are more interracial relationships today.
It her body, let her make all the decisions. Push too hard and the person above that said you will need a divorce lawyer will be correct. Than, you won't even get to watch.