Export a single template file.

def color(colors, export_type, output_file=None):
    """Export a single template file."""
    all_colors = flatten_colors(colors)

    template_name = get_export_type(export_type)
    template_file = os.path.join(MODULE_DIR, "templates", template_name)
    output_file = output_file or os.path.join(CACHE_DIR, template_name)

    if os.path.isfile(template_file):
        template(all_colors, template_file, output_file)
        logging.info("Exported %s.", export_type)
    else:
        logging.warning("Template '%s' doesn't exist.", export_type)