Relationships of T_eff and color in different metallicities from the Dartmouth model. The Sun is marked as a red circle. The error bars of black circles indicates the uncertainty of the conversion for [Fe/H] = 0, whose typical value is ∼0.03 dex. For comparison, the dotted line is from PARSEC model atmosphere (Chen et al. 2014) with [Fe/H] = 0, the dashed line is an empirical relation from Boyajian et al. (2012) with [Fe/H] = 0.