White Golds and Platinum.

Pure Gold is yellow. Always is, always will be. So where do we get white gold?? Usually when we alloy for yellow gold (which is when we mix other metals into the pure gold) we add a mix of (mostly) silver and copper, this makes it harder, polish better and less expensive. When we want white gold we add either Nickel or Palladium instead. Neither is perfect.
Nickel white gold is actually a very light yellow colour, usually it is rhodium plated for a true white colour. As the rhodium, a member of the platinum family, is just a thin coating on the surface of the gold, eventually it gets worn off in spots leaving your jewellery blotchy looking. Some people are allergic to nickel, and might react immediately to their new jewellery, or in a few weeks/months when the rhodium starts to wear off. Nickel gold is a very hard, very finicky metal, sometimes it cracks.
Palladium is a member of the Platinum group of metals, its expensive. This means palladium white gold costs more than nickel white gold. It is slightly grey in colour and softer than nickel white, so it scratches faster and deeper. It is also a great metal to build jewellery out of - very flexible and malliable. It is unlikely you would be allergic to palladium white gold.
Platinum is a separate family of metals, platinum, iridium, palladium... there are 7 total, I cant remember the others off the top of my head....these are the 3 jewellers use. So when I alloy metal for a piece of gold jewellery, I add inexpensive stuff to the expensive gold, 18k gold is 75% gold 25% cheap other stuff. With platinum usually we use 90% platinum, and 10% Iridium, so Ive added expensive stuff to really expensive stuff - that's one of the reasons platinum is so....expensive. Another is that it is much denser than gold, so an ounce of Platinum is smaller than an ounce of gold, a ring that weighs 6 or 7 grams of gold would weigh 10 grams if I made it in platinum. Platinum jewellery has a nice colour, very white, but the metal is very soft so if you have a big smooth shiny band it will mark up much faster than a gold band. Platinum is best used for claws, whether on a single stone or pave work because unlike gold, Platinum does not work harden quickly. Work hardening makes the metal springy, so when the jeweller pushs the gold claws over a diamond they spring back slightly, and then with the every day wear on a ring - all the little dings and whacks it harden the gold more, eventually the stone comes loose. With platinum the claws stay soft, so all the little dings actually push the claws tighter around the stone. In a nut shell, with time gold claws slowly loosen and platinum claws slowly tighten.
So which metal is best? sorry no easy answer. If I was getting a wide shiny plain band my first choice would be nickel white gold. If I was having a handmade eternity diamond ring made? palladium white gold. Am I having a pave dinner ring put together? definitely platinum!