CPD of the three open clusters 1 Gyr or older. Shown are NGC 6811 (Meibom et al. 2011a; Curtis et al. 2019) at 1 Gyr, NGC 6819 (Meibom et al. 2015) and Ruprecht 147 (Gruner & Barnes 2020; Curtis et al. 2020) at 2.5 Gyr, and M 67 (Barnes et al. 2016; Dungee et al. 2022; and this work) at 4 Gyr. The color coding groups cluster data by age. Overplotted is a simplified representation of the emerging cluster sequences by age (solid lines color coded by age). The sun is shown with its usual symbol. Figure C.3 shows equivalent plots in the colors (G_BP − G_RP)₀, (B − V)₀, and (V − K)₀.