According to one example, there is provided a method of calibrating a printing system. The printing system is configured to supply print media and calibration media to a print zone. The method comprises controlling the printing system to position calibration media in the print zone, printing a predetermined set of color patches on the calibration media, measuring color characteristics of the printed set of color patches, and comparing the measured color characteristics with a set of reference color characteristics. The method further comprises calibrating the printing system based on the compared characteristics.