The aqua haired version does exist. She appeared on eBay a month or 2 before Comicon & a few collectors snapped her up. I think that was before so many collectors were aware of TaoBao, but my guess is that she has the same origins as those g4 "prototypes" or ponies that appear to be factory errors, test batches, ect.
The purple haired version was the only one sold at Comicon. At the time these were originally popping up in eBay, we saw both aqua & purple haired ones, so until Comicon happened no one knew which color would be the official release.