Comparison of the instrumental F275W vs. F275W − F814W CMDs of stars in the field of view of the star cluster Lindsay 1 as derived from Method I (top-left), Method II (top-middle) and Method III (top-right). Well-measured stars are colored black, while stars with poor photometry are plotted with light gray dots. Azure crosses mark stars where the F814W magnitude is derived from saturated images. Middle panels: are zoomed-in views of the top-panel CMD around the MS. Bottom panels: compare the region of the instrumental F555W vs. F555W − F814W CMDs populated by bright stars with F555W < −9.75 mag. Calibrated magnitudes and colors are indicated by the top and right axes.