Color–magnitude diagrams for stars in the field at (l, b) = (−1.0°, −8.5°) together with [Fe/H] abundances of stars obtained from spectroscopy (data from Lim et al. 2021). The colored circles indicate the metallicity of stars from metal-poor (blue) to metal-rich (red). The [Fe/H] abundances of stars are clearly enhanced with increasing color. In particular, the metallicity gradient is apparent in the (u − g)₀, (g − r)₀, and (u − i)₀ colors, but is indistinct in (r − i)₀ and (J − K_s)₀. Upper panels: color–metallicity relations (solid black lines) obtained from stars in 12.0 ≤ K_s0 ≤ 14.0. The standard deviation (σ) of the offset between the observed and fitted [Fe/H] values is indicated in the upper left corner. The [Fe/H] of stars is tightly correlated with (u − g)₀, (g − r)₀, and (u − i)₀ colors with a small standard deviation. We note that the dashed magenta line in the (u − i)₀ color represents the color–metallicity relation calculated in Johnson et al. (2020).