Lightness or Darkness. The Tone of color grading refers to the lightness or darkness of the hue, or primary color of the diamond.

For color grading, colored diamonds are placed face-up in a grooved, matte-white, non-fluorescent plastic tray within a controlled environment—a viewing box that eliminates visual distractions and shields external light. GIA also requires a standard geometry between the diamond, the light source, and the observer. The light source is positioned directly above the diamond, and the observer views it approximately perpendicular to the table facet.