Reddening-corrected two-color diagrams (left panels) and reddened CMDs (right panels) for NGC 1903 (upper panels) and the surrounding field stars (lower panels). Right panels: Cepheid variables (pink stars) cross-matched with OGLE catalogs; the young field giants (triangles). The blue and red lines on the CMDs mark edges of the empirical instabillity strip of Cepheids derived by Narloch et al. (2019). The rest of the symbols are the same as in Fig. 1.