Top panel: binned (u_ISL − r)₀ versus (g − i)₀ color-color diagram. The color scale shows the median [Fe/H] in each bin estimated from LAMOST spectra. The black solid line marks the stellar locus for −0.25 < [Fe/H] < −0.20 stars in the range 0.2 < (g − i)₀ < 1.5, noted ZSL_o. The arrows show the color excess vector (E) for the 50th, 90th, and 99th percentiles of the sources’ E(B − V) distributions, corresponding to E(B − V) = 0.03, 0.08, and 0.12, respectively. Bottom panel: normalized histogram of the (u_ISL − r)₀ color difference with respect to ZSL_o for samples of different metallicities, defined with a central [Fe/H] ±0.1 dex. The central metallicity of each sample is labeled in the panel.