Color–color diagram of the selected stars in the field of LH 91. All magnitudes are already corrected for the extinction contribution of our Galaxy, mag and E(m₅₅₅ − m₈₁₄)^MW = 0.1. The arrow shows the reddening vector of E(m₅₅₅ − m₈₁₄) = 0.25 and E(m₅₅₅ − m₆₅₆) = 0.13 for the adopted LH 91 extinction law. The dashed line represents the median photospheric (m₅₅₅ − m₈₁₄) color for the 254 stars with δ₅₅₅, δ₈₁₄, and δ₆₅₆ <  0.05 (gray filled dots). The dotted line shows the model atmospheres of Bessell et al. (1998) computed for the three WFC3/UVES filters. The PMS star candidates with Hα emission excess at the 3σ level are represented with large red dots. The large green dots are the brightest PMS star candidates, with m₅₅₅ <  20 mag. Error bars are also shown.