PACS two-colour diagrams for the Uranian moons. The PACS fluxes are not colour corrected and refer to the PACS standard photometric reference SED ν × f_ν = const. The boxes with the central cross indicate the uncertainty range of the measured colours (determined by log and log, respectively.) The straight lines with the temperature tick marks represent the colours of modified blackbodies calculated according to Eq. (4) for the displayed temperature range and with β as indicated in the upper right corner of each panel. Derived β and T_b are used for a plausibility check of the PACS photometry.