Colour–magnitude diagram showing M_V as a function of V−I_c (in the UCD rest frame). These latter are photometric filters directly computed by PEGASE. We consider 10⁷, 10⁸, 10⁹ M_⊙ as initial stellar masses, and metallicity values [Fe/H] = −2, 0. Here we show only the results for the MKDP IMF plotted together with the quasar data (black cross and plus markers, cross for radio quiet and plus for radio loud quasars) from Dunlop et al. (1993, 2003), Souchay et al. (2015). The data are compiled in Table 3. The CAN IMF, SAL IMF and vDC IMF are shown in Fig. 10. The arrow indicates the time evolution for the UCD models; the black filled circles and squares mark evolutionary time, from left to right: 100 Myr, 500 Myr, 1 Gyr, 5 Gyr, 10 Gyr for [Fe/H] = −2 and 0 dex. The rectangular region indicates where the majority of observed UCDs are located (e.g. Evstigneeva et al. 2008). Since UCDs have a different metallicity, we do not plot individual data points.