The following is a brief explanation of the color grades. D - Best, colorless. Very slight traces of yellow will be apparent to a trained eye. After L, mounted stones will display a tint even to the untrained eye. The term blue-white is a retail expression that implies quality, but has no real meaning.
Diamonds come in various colors such as red, blue, green, black and pink.
Some are natural and some have been laboratory treated. Those that have been treated are worth less than natural colored stones. There are 100 points in a carat, a unit of weight equal to 200 milligrams. A half-carat stone would therefore weigh 50 points. The important thing is to get the weight of the diamond in points, not just the fraction.