Yellow Gold
The gleaming color of gold has been revered throughout the centuries as a symbol of royalty and riches. It is the traditional wedding band metal, and many believe it best reflects the warmth and love of a marriage. Visually, gold's rich color best complements darker skin tones or those with a yellow undertone, and it provides a complimentary setting for rich colored stones such as rubies or amethysts. The reflection of yellow gold on a colorless diamond can make the stone appear yellowish -- and therefore less valuable -- but can also help mask the tint of yellowish diamonds by making the diamond look "relatively" white.
For jewelry, 14K and 18K gold are most often used (the quality mark which you should find inside the shank is simply 14K, 18K, etc.). The "K" indicates the gold's karat, a measure of its purity: A 24K band is pure gold and has the brightest yellow color, but is too soft for most jewelry, especially a ring you will wear every day. A lower karat means metal alloys (copper, zinc, silver, nickel, etc.) have been added to strengthen the metal. These extra alloys diminish the gold's brightness and may be irritating to people with metal allergies, but they greatly enhance the durability of the ring.
Most engaged couples choose 18K gold because it offers a good balance of gold color and strength. Of course, the purer the gold, the more expensive it is. If you can't afford 18K, consider less expensive and stronger 14K pieces.
White Gold
When certain combinations of metal alloys are added to gold, it can produce different colors, as seen in the popular rolling ring wedding band, which consists of three intertwined bands, one each of white, yellow, and rose gold. White metals are white-hot in the jewelry market today, and white gold is the "cool" metal of choice for those who are looking for a less expensive alternative to platinum (white gold costs approximately 45% less than platinum). Don't be fooled by appearances, however: White gold can't match the overall durability of platinum. (Note: When rhodium plating is applied to white gold it produces a platinum-like bright white look, but will eventually scratch and require reapplication .)Platinum
Purer, rarer, and stronger than gold, platinum is an ideal -- if expensive -- choice for your eternal symbol of love. It also has an interesting history: Between 1900 and 1940, platinum was the most popular white metal for jewelry. When World War II began, platinum was declared a strategic metal needed for wartime use (it's as hard as iron) and thus was banned for "frivolous" uses such as jewelry. Now resurging in popularity, platinum has the cachet of all things, well, platinum, whether it's a platinum record or credit card.Platinum's purity makes it hypoallergenic; its strength and density make it the safest choice for holding gems securely and resisting wear and tear (the surface will scratch just like any other metal, but will not dent as deeply). Quality marks for platinum differ by country. Rings that are at least 95% pure are stamped PLATINUM or PLAT (United States), PT 950 or 950 PT (Europe), or PLATINE (Canada). Quality marks for rings that are between 75% and 95% pure include the alloy content: IRIDPLAT (90% platinum, 10% iridium alloy), for example.