KERRBB accretion disk spectra with different masses, accretion rates and black hole spins. Left panel: the initial 10M_⊙ spectrum(blue thick solid line) moves horizontally (i.e., in frequency) when the black hole mass changes (red arrow), and diagonally (i.e., in both frequency and luminosity) when the accretion rate changes (orange arrow). The position of the peak in frequency ν and luminosity νL_ν for a givenspin value follows the same shifting equations found by Calderone et al. (2013). Right panel: when Ṁ increases, the 10 M_⊙ spectrum peak also increases (orange arrow), but less than the increase related to the increase of the spin (green arrow). When a changes the low-frequency part of the spectrum remains constant, but this occurs at frequencies not visible in the figure. The low-frequency flux is produced by the outer regions of the disk, unaffected by the black hole spin. About this effect, see also Fig. 3.