Rotational profiles of blue and red MSTO stars. Left panel: distribution of MSTO stars of NGC 1850A with 3.5 < log g < 4.5 and F569W < 18 in the F439W − F569W vs. EW(Hα) plane. Stars bluer and redder than F439W − F569W = −0.23 are marked by blue and red points, respectively, while Be stars are marked by black points. Right panel: average line profiles of the blue (blue line) and red (red line) samples.