Red and blue pairs classification criterion (central panel): M_g − M_r vs. M_r, where M_g and M_r are the total absolute magnitudes of the pairs in g−band and r−band, respectively. We divide the sample into 10 percentiles in magnitude M_r and then we compute the median color in each percentile (black dots). Subsequently, we fit a linear function (black line) to the obtained points and select the pairs with larger colors as red pairs and with lower colors as blue pairs. Upper and lower panels: total absolute magnitude and total color distributions of the pairs. The vertical blue line in the absolute magnitude distribution corresponds to the median value of this distribution, which is considered to classify higher- and lower-luminosity pairs.