Q-parameter (from our own photometry, Paper I) as a function of spectral type (from Bresolin et al. 2007). Different colors and symbols represent spectral types as indicated in the legend. Size indicates luminosity class (smallest symbols = class V, largest symbols = class I). The WO and the Be stars have been arbitrarily located in the X-axis. The Q color increases as we move towards later spectral types. Most stars with Q ≤ −0.4 are OB, Be, or WR stars.