2.4 Color measurement
The visual color was evaluated in two modes; transmission (Ttran) and Reflection (Rsin) using a Hunter Colorimeter (Hunter Lab, Color Quest XE, Hunter Associates Lab Inc., Reston VA, USA). The instrument was standardized each time with a black and a white color (L = 91.10, a = 1.12, b = 1.26) tiles. D65 standard illuminant, corresponding to the natural daylight, and 10° standard observer were used in the measurement. The color values were expressed as L* (lightness), a* (redness (+) / greenness (-)) and b* (yellowness (+) / blueness (-)). Color values were measured in the means of triplicate measurements.