What is the best quality for a solitaire diamond? There are four factors that affect the value of a diamond. They are referred to as the 4 C’s. They include colour, clarity, cut and carat weight. The value of a diamond comes from all four factors. To explain, the combination of carat weight, colour, clarity and cut gives a diamond its value. For example, take a D colour diamond.  Factor in a Flawless clarity grade. Then, add an excellent cut. Finally, choose a high carat weight. As a result, you have a very expensive diamond!