Like clarity, diamonds are also rated according to color on a letter scale from D to Z. The closer to D the whiter the diamond should be. We think diamonds look best through the letter grade J because they are colorless or near colorless.
Many experts recommend that buying anything from D to H does not translate into a characteristic that can be appreciated without a visual aid, though diamonds in this color range can cost considerably more. Therefore, the greatest value strategy is to buy in the color grades of H, I, and J. Princess cuts, due to their shape, should be purchased in one grade better.
There are two caveats to the above rules. If you are buying a yellow gold setting, the yellow of the gold gets incorporated into the color of the diamond so you can safely buy all the way into the K and L color ranges.
In addition, an optical property of diamonds called blue fluorescence tends to make diamonds in the I, J, K, and L color grades appear whiter. So, if you are looking to save the most money, buy a diamond in this color range with medium to strong blue fluorescence.