Relation between color correction ΔC_438W and Δ(m_275W − m_814W) (top panel) and Δm_814W and Δ(m_275W − m_814W) (bottom panel) resulting from binarity for Y = 0.248 stars. Each symbol corresponds to a combination of spectra as described in Sect. 3.1 and shown in Fig. 3. Each color refers to a given giant star (black: the most luminous giant; red: the intermediate luminosity giant; blue: the giant at the bottom of the RGB), and thus to a given magnitude bin defined in Sect. 3.1. Linear regressions to each set of colored points are shown. For the linear regressions, we also added the point at (0,0) to ensure that all color corrections are negligible in case of low-mass companions. See also, Sect. 3.3.