Effect of dust on optical/near-infrared quasar colors. Only a subset of the dusty QSO-DLAs have near-infrared colors from either 2MASS or UKIDSS. We show where the bulk of the SDSS-DR12 quasar population at 1.5 < z < 4.0 is located in g − r versus u–g, r–i, and J–K_S colors as thegray contours. For illustration purposes we model a redshift track of a composite quasar template (gray solid line) in steps of Δz = 0.5 starting from z = 1.5 to z = 4.0, each step shown by the gray squares. The black dots denote the colors of standard, main-sequence stars from Hewett et al. (2006). Also shown are reddening vectors for a simple system with a DLA at z_abs = 2.5 and a quasarat z_QSO = 3.0, in steps of A_V = 0.25, 0.50, 0.75, and 1.00 mag (red arrows). The dusty QSO-DLAs are overplotted and color-coded as a function of how their underlying background quasars were selected. Red star symbols denote the quasars that were misclassified as stars in SDSS but identified in the HAQ and KV-RQ surveys, blue squares show the sources photometrically selected to be quasars in the SDSS (light) and BOSS (dark) surveys, and orange diamonds denote sources that were observed as part of the SDSS and BOSS surveys but were selected as, e.g., filler or radio sources.