U–I color vs. the observed I-band magnitudefor the AGNs studied in this work. Squares show the targets observed with FORS2 at the VLT telescope, triangles are the AGNs observed with MODS1-2 at the LBT telescope, while pentagons are the AGNs observed with the LDSS3 instrument at the Magellan-II Clay telescope. Three objects from Table 1 have no information on the U-band magnitude and are not plotted here. We do not plot COSMOS1710 since it is not at a redshift of ~ 4.