They are different species.
Golds tend to be a bit smaller at maturity and a lot more aggressive. Black&White(argentines esp) tend to be more calm for handling, get larger and IMO(gleaned from listening to owners talk about what they feed their tegus) seem to eat more fruit.

B&W do have the green heads as hatchlings.

All lizards are individuals.. and I'm certain someone somewhere has a story about THEIR gold tegu who was named Lassie and kissed babies and rescued small children from wells. Also, some B&W tegus can be horrid monsters and never tame down. It's all individual, so I'm speaking ONLY of generalities, and ONLY from my experiance with my own tegus, and talking to other tegu owners.

Hope this helped