Is white gold the same makeup as yellow gold (just a different color), or is it a combination of metals? Is it as precious as yellow gold?
Generally White Gold is sold as 14 or 18 carat. That means the same amount of gold as any other 14 or 18 carat gold (14/24ths or 18/24ths gold) White gold is alloyed primarily with silver and nickle, which makes it white. Rose gold is alloyed with copper, and nickel which makes it pink. Electrum is gold alloyed with platinum. It is not as shiny and bright as white gold, but more expensive. (Because platinum is expensive.)
Remember that gold jewelry isn’t pure gold, it is typically 14k gold. That means it’s only a little more than half gold, 14/24ths. The other metals are often copper (red gold) or silver (white gold), or a mix (gold gold). The precise color of the gold is going to depend on the precise alloy the jeweller uses.
Anything more than 14k gold is going to be much too soft for everyday wear, it would scratch and bend too easily. You might find some 18k jewelry, but almost all is 14k, or sometimes even lower.
The term “white gold” is inexact. It can refer to an alloy of gold with a whitish or silvery precious metal like silver, platinum or palladium, or to an alloy of gold with a whitish or silvery base metal, like nickel or zinc. If you want to know what’s in that white gold ring, you have to ask the jeweler for the exact composition (if you trust your jeweler).
I disagree. I think 18k gold is plenty durable for everyday wear. I don’t think 14k gold became very popular in the U.S. until the huge run-up in gold prices in the early 1980s.
In some countries it is (or was) illegal to sell jewelry as “gold” if it’s 14k. (You can still sell it, but under another name, such as “gold wares”). As of the mid-1980s the standard was 19.2k in Portugal, 18k in France, Italy, Spain, and Sweden, 14k in Belgium, Denmark, the Netherlands, and Norway, 10k in the U.S., 9k in the U.K., and 8k in Germany. These standards may have changed in the last 15 years. In parts of Asia and Africa, the locals won’t buy it unless it’s over 20k (but admittedly, that is quite soft).
I whole heartedly agree, sez the daughter of the custom jeweler, proud owner of several 18 Kt. yellow gold rings that have held up quite well, thank you very much (better, frankly than the silver piece he did in high school). 
White gold is gold alloyed with a higher nickel content than the other golds. Some also has silver in it, but it’s cheaper. I only wear white gold, platinum and silver. I detest yellow gold. To me, yellow gold has always looked cheap. Which is good cuz I have a complexion where yellow gold just doesn’t work. Looks even cheaper on me. I have come across blue gold too now and then and I’m starting to really like it. I’m not sure but I think that is a chromium alloyed gold (?) There is also green gold but I’m not sure what’s in it cuz I think it’s kinda hideous.
I thought Gold alloyed with silver was called “Electrum” and White Gold had to be alloyed with Platinum? Not nickel? Can someone (hopefully a jeweller) clear up this point of confusion?