The bottom part of hair tresses is permed. Afterwards the entire tress is colored in a standardized manner and the initial color value determined spectrophotometrically. To determine the UV protection, the tresses are irradiated for several hours with UV light and subsequently examined spectrophotometrically. To determine the washing resistance/ color fastness, the tresses are treated repeatedly with products or a neutral shampoo and subsequently examined spectrophotometrically. Additionally, the hair color is assessed by hair experts before and after irradiation or following treatment.