The first thing people look for in diamond quality is color.
The scale, from the best color D to the worst color Z, is easy to understand, and most salespeople will immediately refer to a color grade when showing diamonds.
Color is the natural body color visible in a diamond and is the one C determined completely by nature, not man. As a rule, the closer a diamond is to colorless, the more valuable and beautiful it is.
D: Absolutely colorless. The highest color grade.
E: Colorless. Only minute traces of color can be detected by an expert gemologist.
F: Colorless. Slight color detected by an expert gemologist, but still considered a "colorless" grade.
G-H: Near-colorless. Color noticeable when compared to diamonds of better grades, but these grades offer excellent value.
I-J: Near-colorless. Color slightly detectable.
Diamonds graded better than H are colorless or near-colorless and their color is typically undetectable to the unaided eye. I and J colors usually have faint yellow color, especially if you place them into white gold or platinum.
Acting as a prism, a diamond can divide light into a spectrum of colors and reflect this light as colorful flashes called fire. Just as when looking through colored glass, color in a diamond will act as a filter, and will diminish the spectrum of color emitted. The less color in a diamond, the more colorful the fire, and the better the color grade.
Words of caution; lower color diamonds are often made to seem to be superior quality by salespeople by focusing on the clarity - meaning the imperfections in a diamond. It is always advisable to get the highest color you can afford, with a combination of Si1 or Si2 clarity diamond. (Of course, of all the C's, CUT is the most important- releasing the brilliance of the diamond.)
UPDATE - the Logo Pendant Elsa designed for Cancer Care was a huge hit. We have 2 other charities we are considering doing similar projects for.