Left panel: Color–Color diagram. Green points: only RGB stars from the photometric data resulting from statistical decontamination. Blue points: best-fit isochrone model from Section 4.4. The green and blue dotted curves show the linear fit of the green and blue points, respectively. Right panel: plane of $\frac{E(J-H)}{E(J-Ks)}$ vs. $\frac{A_{Ks}}{E(J-Ks)}$. Green diamond: standard extinction law of Cardelli et al. (1989) converted to the 2MASS system according to Table 2 of Catelan et al. (2011). Red and blue diamonds: Bulge extinction law of the ${\text{N}}_{+}^b$ quadrant of Nishiyama et al. (2009) and the average of their four quadrants, respectively. The dotted curve shows the linear fit of these three values. Black point: interpolated value for VVV-CL001.