It refers to weight only . Because weight can hide in different parts of the stone. Some may appear larger than others due to its cut. The color of a diamond has the second biggest impact on its price, after carat weight. Grading color in the normal range involves deciding how closely a stone's bodycolor approaches colorlessness.
Most diamonds have at least a trace of yellow or brown bodycolor.
With the exception of some natural fancy colors, such as blue, pink, purple, or red, the colorless grade is the most valuable. A fancy yellow diamond fetches a higher price than a light yellow diamond. These stones have no imperfections inside or on the outside of the stone under the magnification of a loupe of 10 power. Flawless These stones have no inclusions under a loupe with a 10 power magnification. Slightly Imperfect These stones have very small inclusions which are very difficult to see under a loupe with a 10 power magnification.