Colour-colour diagrams of FR I galaxies in Table 2 in the ${\alpha }_{57}^{144}-{\alpha }_{887}^{1637}$ (or ${\alpha }_{57}^{144}-{\alpha }_{943}^{1367}$) plane. The colour scale denotes the distance from the core relative to the approximate size in Table 2. The solid grey error bar denotes the possible systematic shift of data points due to calibration errors and the thin black error bars denote the rms flux uncertainty. The solid line denotes a pure power-law and the dashed line a JP model. The two lobes are differentiated by either showing a square or triangle. Regions containing the core are excluded from the figure.