Sexual satisfaction is a necessary ingredient of any successful marriage. So if your wife likes black guys because you obviously do not provide her enough satisfaction, then let her go marry one. Because, to be blunt with you, it seems to me your marriage is irrevocably broken. Where does it end once you embark on this slippery slope? Get rid of her and go find someone who can find complete satisfaction in you.
How is this much different than a wife who wants a 3 way with her man and an SP?
Yes, often the wife "enjoys" the physical pleasure from the SP as well. But I bet you, more often than you'd think, the real satisfaction is the enjoyment of being "dirty" with her husband.. And watching her husband get off on it..
While I don't think I could ever watch my wife with another dude, I've certainly fantasized about it at one time or another.. Often our hottest fuck sessions are when she's telling me about other men she's fucked and what their cocks felt like and how dirty she was etc.,. And, despite my SP fetish, I believe the two of us are very much happy in our marriage..
If the OP thinks he's man enough to watch his wife with another man, and still love and adore her, then all the power to him..
Besides, women find courage, power, and confidence attractive in men.. What shows more confidence than letting a physically larger man fuck your wife?