J - This is average, it has a slightly visble tinge of yellow or brown. The lower end of the scale sometimes moves into fancy colours. Argyle Diamonds grade their Champagne and Cognac Diamonds in a scale of 1 - 7. A diamond described as a C7 would be a cognac diamond, rich brown. A C3 would be a light to mid champagne colour.
Diamonds come in fancy colours.
Various shades of Pink, Green, Blue, Yellow etc. These have their own specialized scales of grading. When relating to the price of a diamond the term cut is relating to the quality of the cut rather than the shape. The quality will effect the price. Unless otherwise described the diamonds I have listed for sale have an good average cut.