A chromaticity instrument (CR-400, Onica Minolta Co.,
Japan) calibrated using a white standard board was used to
measure the color of the sample surface. Readings were
expressed in the CIE1976 Lab scale, where L measures
lightness, with 100 being white and 0 being dark; the a
value measures green () to red (þ) and b represents blueness
() to yellowness (þ). The hue angle (h) and the
chroma (C) were calculated according to the values of
L, a, and b as follows