I like the fact that she has no idea that you want to watch her have sex with a well endowed black man. She has no idea what's really going on in your mind. For a white guy to tell his white wife that he wants to watch her have sex with a black guy can be very difficult.
I like that you told her they made a mistake with the dildo. I think you should ask her what she's fantasizing about when she's using the black dildo.
A cuckold once said that he always had this fantasy of watching his pretty blonde wife have sex with a black guy. He said that when he finally saw it happening in real life, it was so much better than what he ever imagined. He was so aroused that he just ejaculated without even touching himself.
I hope you get your wife to have sex with a black guy. From what I have seen over the years, if a woman is not willing to swing, then she will probably not be open to cuckolding.