Those gold colored fishes are color morphs of standard Arothron species. It's a phenomenon similar to albinism, leucism or xanthism, but I'm pretty sure no one knows yet for sure, which of the three effects exactly. Just like albinos they are born golden and grow up golden. This phenomenon is not limited to puffers, but occurs in many other fishes, e.g. there is a yellow/golden variety of the usually spotted Gymnothorax miliaris and there are golden archers (true xanthism here), and many more.
Now the interesting part about puffers: The golden ones are not color morphs of one, but of TWO puffer species: Arothron meleagris and Arothron nigropunctatus. Both morphs are hard to tell apart, but the golden A. meleagris has a few tiny white spots often in groups and often on the back, while the golden A. nigropunctatus has exclusively black spots.
A. meleagris:
http://filaman.ifm-geomar.de/Photos/Pic ... at=species
look at the fins!
http://www.saltwaterfish.com/site_11_03 ... enpuff.jpg
Look at the fins of this one and the back
A. nigropuctatus
http://filaman.ifm-geomar.de/Photos/Pic ... &TotRec=18
can be much more yellow, best picture I know is in Mergus aquarium atlas #6.
Give a man a fish, and he'll eat for a day. Give a fish a man, and he'll eat for weeks.