Color variations in two methods. In the main panel, the black and red data points are for RQ and RL quasars, respectively. The uncertainties are shown with gray error bars. The sources in regions I and III have consistent color variations from the two methods, and thus were considered in our analysis. In contrast, the color variations of objects in regions II and IV are uncertain for various reasons (see the text for details), and thus were excluded from the analysis. Two side panels show the distributions of ﹩{\alpha }_{{\rm{b}}}-{\alpha }_{{\rm{f}}}﹩ and α_d, from which it can clearly be seen that most sources show the BWB trend, and there is no significant difference between RQ and RL quasars.