a) J−H versus H−Ks color−color diagram of bright main-sequence stars based on the 2MASS measurements. The solid curve indicates locus of main-sequence stars while the dotted curve indicates that of giant stars (Bessell & Brett 1988). The solid arrow shows the interstellar extinction vector for A_v = 1 mag, using the Weingartner & Draine (2001) Milky Way model of R_v = 3.1. b) Same as a), but for the IRSF measurements. The objects above dashed lines are removed from our main-sequence sample because they might be giant stars.