Spectral colors evaluated as the ratio of the fluxes in the 0.3−3 keV (S) and 3−10 keV (H) bands. For the other datasets we used the best-fit models reported by Parmar et al. (2001) (Beppo-SAX), La Parola et al. (2003), Dubus et al. (2004) (Chandra), Middleton et al. (2011) (XMM-Newton), and Isobe et al. (2012) (Suzaku). The error on the ratio has been evaluated assuming the fractional error on each band to be equal to the fractional error on the total flux, when reported, or assuming an arbitrary error of 5% on the flux in each band when the error on the flux was lacking. All fluxes are corrected for absorption.