A Zeiss Microsystems MPM 800 microspectrophotometer coupled to a Zeiss axiotron microscope was used to undertake colour measurement in reflectance mode, with an Epiplan 50x objective, a circular 1 mm diameter window (diameter spot area: about 0.4 mm). The spectral range is between 380 and 800 nm with 5 nm steps. The mean of ten measurements was taken. A white Opal glass was used as background material. A Lambda Scan 1.60 program from Zeiss was used.