This provides a more precise and accurate description of gems. When shopping for sapphires, evaluate color by taking into consideration hue, tone and saturation. Pure, vivid colors are far more desirable than dull or milky colors. Saturation is the brightness or vividness. The darkest is black.
Tone is the degree of lightness or darkness.
Judging the tone of a stone is difficult because it does not display a single, uniform tone. All basic blue sapphires exhibit some other colors or hues. To determine the hue, again, look for the dominant color in the face-up view of the stone. When you move the stone in different directions you may see the different colors. Both intensity and tone of color can be significantly affected by the proportioning of the cut.