Quality of the spectral flux calibration. Top panel: comparison between observed and synthetic colors (ɡ – r) indicated with black dots, (r – i) with red squares, and (V – i) with blue triangles. Synthetic colors are computed using WFCCD spectra and the CSP-I system response functions (see Krisciunas et al. 2017, and references therein). Bottom panel: residual between the observed and synthetic colors vs. synthetic colors. The dashed line has a slope of unity.