I was undercompensated by a company HQ in Atlanta, GA but I live in Colorado. Do I need a GA attorney?

That depends on whether the company has sufficient contacts with Georgia for a Georgia court to exercise jurisdiciton over it.  You didn't set forth the circumstances giving rise to your claim, but if it arises out of a contract which was to be performed in Georgia, Georgia would probably be able to exercise jurisdiction (assuming that you have no agreement with the company which requires that claims be asserted in some other venue).