Comparision of the t_rps values with the observed color and the cluster-centric distance. Left: observed g − i color as a function of the best-fit t_rps value from the models. The dashed red and dotted blue curves show the model integrated g − i color for the median values of the UDGs and diffuse galaxies, respectively, as discussed in Sect. 6.5. The solid and dot-dashed black curves indicate the models for a representative dwarf and Milky Way-like galaxy, respectively (Boselli et al. 2014). The solid green line is the quenching time model for a red UDG from Chan et al. (2018) based on the FIRE simulation (see their Fig. 4, model m11b). Sources with only upper limits in the color or with t_rps uncertainty > 0.5 Gyr are excluded from this plot. This plot also does not include one galaxy (ID 2365), which has t_rps ≈ 8 Gyr, a large error bar in the color, and a very crowded field upon visual inspection. Right: t_rps values with respect to the projected distance from the cluster center, in units of the cluster virial radius (R_vir = 1.55 Mpc; Ferrarese et al. 2012). The blue-shaded area marks the region of ongoing RPS (t_rps between 13.3 and 13.7 Gyr). The solid black line and the red-shaded region give the linear regression best fit and the 3σ scatter, respectively, as given in Table 4. Sources with t_rps uncertainty > 2.5 Gyr are excluded from this plot.