CMD of the SNR G22.7-0.2. Black points denote the 2MASS data, and grey points denote the UKIDSS data. The borderline is at K_S = 11.8 mag. Blue points mark dwarfs, and magenta points mark giants which are picked through a comparison with the Gaia parallaxes (Sect. 3.2). Red cubic curves roughly outline the range of RCs. The points located between two red curves are thought to be RCs. The RC ridge is described by red points which is derived by the normal parameter estimation in this case. Red dashed line represents the cutoff magnitude which is 13.8 mag here.