# This routine modifies an RGB color (returned by winfo_rgb),
# applys a factor, maps -1 < Color < 255 and returns new RGB string

    def transform(self, rgb, factor):
        retval = "#"
        for v in [rgb[0], rgb[1], rgb[2]]:
            v = (v*factor)/256
            if v > 255: v = 255
            if v < 0:   v = 0
            retval = "%s%02x" % (retval, v)
        return retval

# This routine factors dark, very dark, light and very light colors
# from the base color using transform

    def set_colors(self):
        rgb = self.winfo_rgb(self.base)
        self.dbase  = self.transform(rgb, 0.8)
        self.vdbase = self.transform(rgb, 0.7)
        self.lbase  = self.transform(rgb, 1.1)
        self.vlbase = self.transform(rgb, 1.3)