How to Ruby Grading? What is ruby color grading system?

One of the most important challenges facing gem dealers is how to grade rubies into various categories. The most important problems found in trying to develop an effective ruby grading language are the lack of understanding among gem dealers about color terminology as used by color scientists. As a matter of fact, the principal difference between a fine ruby and a lower graded stone is the color saturation or chroma and intensity of the hue (dominant color) rather than a color or hue shift.

Ruby buying guide