So am I understanding that your belief is that a black person moving into a white neighborhood would lower the property value
Not necessarily. Depends on how steeped in the CULTURE he is and how much he identifies with the norms, mores and ways and memes of the CULTURE. Its a spectrum thing of course, but even a hint can turn out to have a negative impact.
Keep in mind, this CULTURE is relatively new. 50-70 years ago, they would have never tolerated this amongst themselves. Alas, what we have now seems to have staying power.