Color–color diagrams of the 18 BHB stars (black circles) on the LoS of (l,b) = (39,50), and 24 contamination stars (blue points) on this LoS, selected from Smith et al. (2010). The magenta arrows present the reddening direction, the starting point of each arrow is the median value of the color indexes of the 18 field stars, and the terminal is the reddened original point with R_V = 3.1 and E(B − V) = 0.1.