(u − r) vs. (g − i) color–color diagram in miniJPAS for point-like sources with r <  21.5 mag (red dots). The gray area defines the bluest point-like sources with (u − r)< 0.80 mag and (g − i)< 0.25 mag. The 33 sources in this area are classified from the SDSS spectrum as 11 white dwarfs (eight with a H-dominated atmosphere, orange dots; two with a He-dominated atmosphere, purple dots; and one metal-polluted DZ, black dot) and 22 QSOs (green squares). The expected colors from theoretical cooling tracks for H-dominated and He-dominated atmospheres with logg = 8 (Sect. 3) are shown with the orange and purple lines, respectively.