In golden South Sea pearls gold vs yellow is the biggest distinction and is also the reason there are so few farmers that specialize in golden South Sea. Gold is the most valuable color in South Sea -- it commands the highest prices. Yellow, on the other hand, is the least valuable of all South Seas and commands the lowest prices. The bulk of any gold South Sea harvest is yellow. Jewelmer is probably one of those rare exceptions but only because they've been perfecting their gold brood stock for more than a decade.
The difference in cost from a light yellow to a deep gold, even if all other factors are equal, could be 10 to 20x. This is one of the reasons dyed golds are so dangerous if the treatment isn't disclosed. Dyed are almost always dyed deep gold and come from light yellow.
It's easier to show the difference than explain the difference. The pearl on the left is what I would consider medium gold. The pearl on the right is yellow. I've included a 14k cup because the cup is gold. When golden South Sea are photographed with actual gold in the same photo, you can usually tell the tone.
Sorry for the camera phone shot. Angela is taking a week off after Hong Kong.