The diameter of measuring aperture at spectrocolorimeter ColorQuest XE (HunterLab, USA) was 9 mm and measurement conditions were set to value of d/8. Internationally recommended standardized white light termed D 65 was used as a contractual white light used for measurements. The spectrocolorimeter is equipped with four colour spaces. Colour space CIE L*a*b* (1976) was used for the measurements where coordinate L* represents degree of brightness, coordinates a* and b* describe the colour hue and the hue angle H can be calculated as H ¼ arctan b*/a*.