Generally, L ⁎ , depending on reflectivity of determined surface, is used to express luminosity of sample surface, a ⁎ and b ⁎ indicates chromaticity on a green (−) to red (+) axis and chromaticity on a blue (−) to yellow (+) axis, respectively ( Du et al., 2009 ). L ⁎ , a ⁎ and b ⁎ values were determined using a CR-300 chroma meter equipped with a CR 300 measuring head (Minolta, Hong Kong).