Maybe it's because white is the color of mourning and death in most of Asia.
and on a side note, we ran into the fact that for some reason hmong dont buy cornish x. Why? I don't know, maybe cause they can buy them in the store?! but I sold ALL of our unwanted roos to the hmong and they wanted the rest of the flock also. our last batch of fatties(cornish X) that we raised to sell, we have sold only a few. no one wants them. why? so next year we're going with possible the delawares not sure on that YET. then we'll see what happens.
I have run into this as well, but I think it's more the color of the birds as opposed to CX, specifically. They won't buy white birds. So...Delawares may not do any better for you on that front! If I had red or buff cockerels, I could sell every one of them at a premium, and they would drive out to the boonies where I live to pick them up!