Every Hydeblanc diamond has been assigned a color grade by the GIA, because GIA’s color-grading scale for diamonds is the industry standard; almost every diamond sold today is rated using the GIA color scale, whether it was actually certified by the GIA or not.
The GIA grades diamonds on a scale of D (colorless) through Z (light color). All D-Z diamonds are considered white, even though they contain varying degrees of color. True fancy colored diamonds (such as yellows, pinks, and blues) are graded on a separate color scale.

Below is the GIA diamond color chart:

diamond color grading