Observed colors for stars in Westerlund 2, with data for the Wolf-Rayet stars WR 20a and WR 20b plotted as circled yellow points. The intrinsic relation for dwarfs is plotted as a solid black curve, with the same relation reddened by E_B − V = 1.65 as a gray curve. Reddening lines of slope E_U − B/E_B − V = 0.64 are plotted relative to the hottest O stars and A3 dwarfs (red lines), and B5 dwarfs (blue line). A similar reddening line of slope E_U − B/E_B − V = 0.75 is shown for the hottest O stars (green line).