Difference, Δ = m_synth − m_JKC, versus color index, JKC_bv = (B_JKC − V_JKC), for all data identified in APPLAUSE DR3 that were cleaned and matched to Gaia DR3 stars using synthetic Johnson-Cousins magnitudes from Gaia DR3. Left: plate 12368, Großer Schmidt-Spiegel, Hamburg Observatory, 12 Dec 1968, Kodak IIa-O with filter GG13(=385), scan 14850 (color term 0.826), and scan 14851 (color term 0.704). Right: plate 11626, Großer Schmidt-Spiegel, Hamburg Observatory, 5 Oct 1964, Kodak 103a-D with filter GG11, scan 14057 (color term 0.013), and scan 14058 (color term 0.004). We used an air mass of 1.25 for the analysis in both cases. The ranges of the y-axes were changed in comparison to Fig. 5.