E(B − V)^host from the g − r colors measured between 0 and 20 d after r-band peak brightness and corrected only for the MW extinction. The blue curves represent the intrinsic color and its uncertainty (obtained from the dereddened g − r colors of six SNe Ic-BL from the literature (see Prentice et al. 2016, their Fig. 10). Each SN color is fit with a low-order polynomial (colored curves with color matching the symbol color) in order to compare it to the intrinsic color and compute the average g − r color excess.