def add_lane_lines(img, lane_line_img):
    """
    Colors lane lines in an image
    """
    ret_img = img.copy()
    ret_img[(lane_line_img[:, :, 0] > 0)] = (255, 0, 0)
    ret_img[(lane_line_img[:, :, 2] > 0)] = (0, 0, 255)

    return ret_img