Correlation between EW₆₆₁₄ and E(BP-RP). The top panel shows all sources within 600 pc. The middle and bottom panels focus on four molecular clouds: Perseus, Taurus, Orion A, and Orion B. Each sub-panel displays the linear fit for the respective cloud, along with the Pearson correlation coefficient, slope, and number of stars. Error bars indicate the uncertainties in EW₆₆₁₄ and E(BP-RP). A typical EW₆₆₁₄ uncertainty of 0.02 Å, represented by the black error bar, is shown in the bottom right corner of the top panel.