Nothing at all.Just don't rock the boat by indulging in the fantasy.Let it remain just a passing fantasy.
Instead of looking elsewhere for satisfaction,,due to natural boredom with the same partner,,take her out on a vacation,try new techniques. Is she looking for fresher experiences? If she is faithful to you,why nor reciprocate?
You should find a black couple that will swing with you and your wife. That way, there's something for everybody.
You may think of getting friendly with a mixed-color couple, preferable a white male and black female. Interact with them in depth and you may find out what you want. I am a married white female 38yo but find a black cock most satisfying which my hubby arranged for me on occasional sessions!!
In urban areas black whores tend to be cheap and plentiful. Rent one you like the looks of and blow a load. Just be careful - condoms are a must and take care you don't get rolled.