It would be funny if the only reason Apple had not permitted pre-ordering the white ones is if they had messed up something to do with distinguishing black from white devices, in the model numbers, on boxes or in the devices' internal ID-data storage. I have visions of a hastily assembled bunch of senior clerks at Foxconn busily creating lists of ranges of serial numbers.... hopefully not storing them on ATT servers...
Anyway if it just turns out that they had some white phones in the early production runs that discolored or cracked or whatever, then it's better they halt processing of orders for the white ones until they get the production issues sorted out.