the colour of the Dutch Royal House. Shirts are normally made of a polyester mesh, which does not trap the sweat and body heat in the same way as a shirt made of a natural fibre. Most professional clubs have sponsors' logos on the front of their shirts, which can generate significant levels of income, and some also offer sponsors the chance to place their logos on the back of their shirts. Depending on local rules, there may be restrictions on how large these logos may be or on what logos may be displayed. Competitions such as the Premier League may also require players to wear patches on their sleeves depicting the logo of the competition. A player's number is usually printed on the back of the shirt, although international teams often also place numbers on the front, and professional teams generally print a player's surname above their number. The captain of each team is usually required to wear an elasticated armband around the left sleeve to identify them as the captain to the referee and supporters. Most current players wear specialist football boots, which can be made either of leather or a synthetic material. Modern boots are cut slightly below the ankles, as opposed to the high-ankled boots used in former times, and have studs attached to the soles. Studs may be either moulded directly to the sole or be detachable, normally by means of a screw thread. Modern boots such as the Adidas Predator, originally designed by former Liverpool player Craig Johnston, feature increasingly intricate, scientifically aided designs and features such as air pockets in the soles and rubber "blades" on the sole rather than studs. The blades have been the subject of controversy as several top managers have blamed them for injuries both to opposition players and to the wearers themselves. The rules specify that all players, regardless of gender, must wear the same kit, however in September 2008 the Dutch women's team FC de Rakt made international headlines by swapping its old strip for a new one featuring short skirts and tight-fitting shirts. This innovation, which had been requested by the team itself, was initially vetoed by the KNVB, Dutch football's governing body, but this decision was reversed when it was revealed that the FC de Rakt team were wearing hot pants (very short shorts) under their skirts, and were therefore technically in compliance. Other equipment