Carat is a unit of measure for diamonds, while karat is used in reference to gold. Whether you use yellow gold, white gold, platinum or a combination of all, the setting is how you show off the fantastic diamond you've found. With gold, the karat number represents the percentage of gold in the metal. The higher the number, the more gold there is and the more delicate the piece is. Your ring should be stamped on the inside with the karat weight.
Yellow gold is the most common and is less brittle than white.
The higher the karat number, the more intense the color will be. White gold is stronger than yellow but is also more brittle. Platinum is becoming almost as common as gold. Its popularity has been growing partially because it is a very durable, hard metal. Unlike some other metals it is virtually hypoallergenic, so almost no one will have difficulty wearing it.