2.3.1. Colorimetric Properties and Visual Appearance Evaluation

The color properties of each formulation were determined in the CIEL\*a\*b\* color space using a Konica CM-3600d ColorFlex-Diff2, HunterLab, Hunter Associates Laboratory, Inc, (Reston, VA, USA), using the standard rectangular specimens as the sample. The instrument was calibrated with a white standard tile and the color coordinates: L\* (lightness), a\* (redgreen) and b\* (yellow-blue), and yellowness index (YI) were measured. Measurements were carried out in quintuplicate at random positions over the sample surface. For the visual appearance evaluation, film samples were placed on a background image, to evaluate their transparency and the change in tonality due to the incorporation of GR. All samples were photographed in the same ambient light conditions and the evaluated films presented a uniform and constant thickness of 200 µm.
