Completeness and purity of the overlapping BHB sample as a function of G for BHB stars of different stellar colors. The top panel shows the ratio of BHB stars found from the same combined catalog (Gaia XP spectra×SEGUE survey) by us and by Barbosa et al. (2022). The middle panel presents the purity defined as the proportion of low log g stars in our 1903 BHB candidates that have a measurement of LOGG_SPEC in the SEGUE survey. The bottom panel displays the purity defined as the proportion of metal-poor stars in our 4332 BHB candidates that have a measurement of [Fe/H]_LAMOST in the LAMOST OBA-type stars catalog. The dashed black lines describe the completeness and purity as a function of G without the consideration of stellar color. The completeness declines rapidly as stars become fainter, while for the purity it remains almost constant with minimal variation.