Dressage tack is usually black in color, with a white square pad, giving a formal look. Except for the upper levels, where a double bridle is permitted, horses may only be ridden in snaffle bits. There are strict guidelines as to what type of snaffle may be used, and the more severe types (such as any twisted bit) are prohibited. If a double bridle is used, a plain cavesson or crank noseband must be worn. With a snaffle bridle, the rider is also free to use the drop, flash, or grackle noseband, with the flash and plain cavesson being the most common. Breastplates are also fairly common in dressage at an event, despite the fact that they are not seen at regular dressage shows. Other forms of equipment, such as martingales, protective boots, gadgets/training devices, bit guards, polo wraps, or tail wraps, are not allowed during the test.