You should not push her into it. But if you want her to take on black lovers and experience their supriority my suggestions is as follows:
Befriend a good candidate for a black lover for her; explain that you want him to become your wife's lover; have him come over regularly and befriend the both of you; have him start to openly flirt with her in front of you and you don't say *******; if your wife asks you how you could let him flirt with her, tell her that you simply don't have it in you to say no to him; then tell her if she started flirting back you would understand as that is a normal progression when the hubby is not stepping in to stop it; continue to be timid around him in front of her and encourage him to continue being flirtatious and more aggressive with it; she's start losing respect for you as a man and start lusting for him; before you know it you'll be regretting the situation you put yourself in (her man-less hubby that helps arrange her dates).
This is coming from an Arabic/Muslim guy that knows all too well the way Muslim females think, etc.