Intrinsic H, J − H and H  −  K_S colors of stars in the ONC as function of T_eff (from top to bottom respectively). Circles, crosses and squares represent stars with spectral types provided by Da Rio et al. (2012), R07 and S04 respectively, while the error bars take into account the uncertainties in both the extinction-corrected photometry and the synthetic photometry. Red solid lines show our fits, together with the corresponding 95% confidence bands (dashed red lines).