Gold
Pure gold is 24 karat and too soft for everyday rings, so it is mixed with other metals. 18K is 75% gold and has a richer color; 14K is 58.5% gold and is a little harder and more affordable.
Yellow gold
Gold alloyed with silver and copper. The classic warm tone, and it ages gracefully.
White gold
Gold alloyed with white metals and usually finished with rhodium for a bright white look. The plating can wear over time and can be renewed.
Rose gold
Gold alloyed with more copper, which gives its pink tone. It is durable and flatters most skin tones.
Platinum
Platinum is naturally white and, in jewelry, usually about 95% pure. It is dense and durable, hypoallergenic, and develops a soft satin patina that can be polished away. It is heavier and generally costs more than gold.
Not sure which to choose? Look at the stone first. Rose gold flatters pink diamonds, yellow gold warms yellow ones, and platinum or white gold suits a colorless stone.
Care
Have your ring cleaned and inspected once a year, and take it off for heavy work, swimming and cleaning products.