The main reason for this is obviously due to rarity in nature, but current market conditions at any specific time plays a very important role. Some sizes and shapes fall in and out of demand due to what is fashionable or considered affordable in society. Because of this, some size groupings for a given shape may have a higher demand and price per carat than one expects, given its rarity in nature. A diamond that is 1 full carat in size, has a higher demand, which causes it to be priced higher. The result is rough stones that could possibly have been cut into beautiful smaller stones are usually cut into not so beautiful 1 full carat stones to get into the higher price range.
Diamonds are color graded by a gemologist against a master set of colors. .
I-J are are not quite as bright or have very slight hardly noticeable tint. K-L have a slight tint even the average person will begin to notice. M or Lower the color will be noticed. . Diamonds occur naturally in all spectral colors, from red to blue, however the most commonly occurring colors are yellow and brown. They began at D in case a whiter diamond was later found.