Yep apparently it's not just hair: there will definitely be new hairstyles and colors, but there may also be new jewelry (earrings and noserings, I'd assume), and maybe even tattoos to choose from. And the most interesting piece of news is that the hair changing won't take place outside of the game, in a menu or some such, but at ingame barbershops.
Strange. Will there be a barbershop inbetween the swords and wands shops in Orgrimmar? Or maybe new hairstyles will be confined to the new expansion, and the barbershops will appear in Dalaran only. Either way, Salthem says the design is still being planned, so we're a long way off until getting concrete information on this. Hopefully, Blizzard has gotten clued in to how excited players are about more customization option, and we'll all get something cool when the expansion eventually hits.