First, if the images are real, he's not sending them to appease any social images, he's just using the image held in a persons mind to reinforce the fact that it really is God visiting them. He could also appear as a burning bush, a bright light, or a purple hippopatamus for all that matters. If a person thought Jesus was a purple hippo, God would present himself to them as a purple hippo. Plus, why would God send an image to everyone? If everyone receives an image then he proves his existence, which is kinda what he doesn't want. The whole reason that our God image is of a white God is because we are a white society. In Africa, there are instances of dark-skinned Marys and Jesuses (awkward plurals), in Asian countries, of Asian forms of them, so on and so forth. That was both a missionary tactic (Look, he's like you, worship him) and just an assimilation change that the culture forced on the religion.