When jewelers speak of a diamond's color, they are usually referring to the presence or absence of color in white diamonds. Color is a result of the composition of the diamond, and it never changes over time.
Because a colorless diamond, like a clear window, allows more light to pass through it than a colored diamond, colorless diamonds emit more sparkle and fire. The formation process of a diamond ensures that only a few, rare diamonds are truly colorless. Thus the whiter a diamond's color, the greater its value.
To grade 'whiteness' or colorlessness, most jewelers refer to GIA's professional color scale that begins with the highest rating of D for colorless, and travels down the alphabet to grade stones with traces of very faint or light yellowish or brownish color. The color scale continues all the way to Z.
Diamonds graded D through F are naturally the most valuable and desirable because of their rarity. Such diamonds are a treat for the eyes of anyone. But you can still obtain very attractive diamonds that are graded slightly less than colorless. Diamonds graded G through I show virtually no color that is visible to the untrained eye.
The Impact of Fluorescence
Fluorescence is not directly related to a diamond's color. This separate characteristic refers to the diamond's ability to fluoresce under ultraviolet (UV) light. Our sun emits some UV light, but it is usually not great enough to detect fluorescence. When exposed to UV light, many diamonds will give off a distinctive glowing blue coloration. Althought, fluorescence may be displayed in various colors, blue is the most common in diamonds. The fluorescence of a diamond is defined by its intensity as either None, Faint, Medium, Strong, or Very Strong.
The impact of fluorescence on price depends on its noticeably. Faint fluorescence has very little effort on a diamond of any color, and therefore has no effect on value. For some higher color stone (D-G) strong fluorescence may give the stone a milky white appearance, which greatly lowers value. Fluorescence can add value to lower color stones, such as I and lower, as it gives these stones the appearance of being whiter and brighter.