﹩r-W1﹩ (AB) color as a function of r − K (AB) color for the 1891 X-ray sources with SDSS, UKIDSS, and WISE counterparts that have K-band and W1 detections and UKIDSS (WISE) coordinates within 2″ (3﹩^{\prime\prime} ﹩) of the SDSS position. Many of the stars can be identified by the distinct track they occupy in this color space (LaMassa et al. 2015b).