Colored gemstones like Rubies & Emeralds are known for their pleasant color, therefore richer and better the color shade better the quality ! Color of a gemstone is determined by 3 main factors:
HUE: It can be described as the basic color of the gemstone. Ex: Yellow, Blue, Green, etc. Hue is further classified into Primary and secondary hues. Ex: Bluish Green, here Green is the primary color and Blue is the secondary color.
TONE: is the amount of black in a specific color. Its is measuring a color on the scale from light to dark.
SATURATION: It is the amount of hue in a color. In common words it is a transition from Black & White to Color.