FWIW, I don't think that it's necessarily a cross and believe it could just a complete lack of breeding standards. The average person with a fish tank wouldn't care about the quality of the fish. 
Ron & Josh, isn't there some other mbuna with it's body half colored like that? I swear I've seen something similar before...
Yes there are. I can't think of any with yellow/white off hand though. One example would be G. moorii. Another would be the guy top center in this photo (having a brain fart right now and can't recall what the scientific name is ...):

Ron, is the fish in that photo the "Flame Back Zebra" that was swimming around several years ago? I brought in wild stock several years ago and they were distributed in our area. It is currently called Metriaclima glaucos "Flame back" from Kanjindo Rocks.
As for most of the yellow/white patterned Labidochromis at LFS are most likely just poor bred stock.
There are several variants of the Labidochromis caeruleus "White" that come from different collection points.
Some are all white; some have a pale yellow above the white; some are a blue tinted white; and there is the Labidochromis pallidus which is white with just a small yellow cap on the head.
The majority of white/yellow labs in LFS are not these wild type variants though...just bad breeding stock as I already mentioned.