Diamonds are graded on a letter scale from D to Z: D, E, or F diamonds have no color detectable to the unaided eye;  grad G, H, I, or J are nearly colorless, but a trained gemologist can detect a slight yellow cast. J through Z colored diamonds have yellow or gray color visible to the unaided eye. Diamonds rated lower than I have color that is detectable even to the untrained eye. Those rated J to M have a trace of color, while any diamond with an N or higher carries a noticeable yellow tint