Sometimes when a rough diamond is being cut, the color will improve. The skin on a rough crystal when removed, will sometimes present a much whiter or more colorless stone than originally perceived. Also, as material is removed from the diamond, layers of color also come off. Imagine a very thin sheet of clear plastic that has a slight tint of yellow in it. As you stack the sheets of plastic you will see the yellow tint become darker. After a hundred sheets you might see a very obvious shade of yellow that was very difficult to detect through five sheets. A larger diamond as a result has more distance for the light to travel and therefore more light absorption (and re-emission). The exception again is the colorless diamond that contains no other color-altering-elements and is structurally ideal in its isometric crystal form.