Freshwater dwarf puffers never exceed 1.5". The first puffer you bought at Petsmart may be a Green Spotted puffer (brackish, up to 6.5") or a South American puffer (freshwater, up to 3"). True dwarf puffers (Carinotetraodon travancoricus) can be several shades of yellow/brown, and will often "change color" depending on there mood. Also, my male dwarf is a lot brighter than my female.
Here's a great link for helping determine what kind of puffer you have. It has great pics and plenty of info on freshwater and brackish puffer.