The more colorless a diamond is, the more it shines and the more intense the color analysis inside it is.
Colorlessness increases gradually, from slightly colored diamonds (Z) to completely colorless ones (D).
D/E/F = colorless diamonds
G/H/I/J = almost colorless diamonds
K/L/M = diamonds with a subtle color hue
N/O/P/Q/R = diamonds with a very light color hue
S/T/U/V/W/X/Y/Z = diamonds with a light color hue