The color index vs. magnitude diagram for SN 2006aj (3.5 d  < t − T₀ < 18.7 d). a) The colors in the band longward of the region, in which line blanketing dominates. b) The colors in the region with line blanketing. Error bars of the color index are included. The data were corrected for the reddening and light contribution of the host galaxy. See Sect. 3 for details. (This figure is available in color in electronic form.)