Selected PPCs for three asteroids: (a) (66) Maja, (b) (142) Polana, and (c) (207) Hedda. These spectral types are given in parentheses based on the Tholen and Bus-DeMeo classifications. The filled red circles are R_C-band P_r data acquired in this study, while the green crosses are V-band P_r data from previous research. These data points were fitted using the modified linear-exponential function (see Eq. (1) in Sect. 2.2) despite the discrepancy in the filters. The fitting profiles are shown by the dashed lines.