The aim of this work is to evaluate the performance of photometric metallicity [Fe/H], determined based on V-band light curves photometrically transformed from the gr-band light curves. We tested this by using a set of homogeneous samples of fundamental mode RR Lyrae located in the Kepler field. It was found that the color term is necessary in such photometric transformation. We demonstrated that when including the color term the determined photometric [Fe/H] are in good agreement with the spectroscopic [Fe/H], either based on the calibrated or the transformed V-band light curves. We also tested the impact of Blazhko RR Lyrae in determining the photometric [Fe/H], and found that Blazhko RR Lyrae can give consistent photometric [Fe/H]. Finally, we derived independent gVr-band [Fe/H]-φ 31-P relations(where φ 31 and P are the Fourier parameter and pulsation period, respectively) using our light curves. The V-band relation is in good agreement with the most recent determination given in the literature.