(a) Graphics illustrating where various states appear within the power colour diagram. The area of overlap between the hardest and softest states is also indicated. (b) Power colour–colour plot for all observations of the transient objects within the sample with labels indicating 20° azimuthal or ‘hue’ regions from which the power spectra given in c were found. The plot is colour-coded for each 20° bin with the same colours used in c. (c) Example power spectra for each of the 20° ranges of hue around the power colour–colour diagram. Colours and indices refer to the 20° angular bins used in b. Further examples are given in the Appendix.