This is what the FIFA rules say about it:
Basic equipment
The basic compulsory equipment of a player comprises the following separate
items:
• a jersey or shirt with sleeves – if undergarments are worn, the colour of the
sleeve must be the same main colour as the sleeve of the jersey or shirt
• shorts – if undershorts or tights are worn, they must be of the same main
colour as the shorts
• stockings – if tape or similar material is applied externally it must be the
same colour as that part of the stocking it is applied to
• shinguards
• footwear
Shinguards
• are covered entirely by the stockings
• are made of rubber, plastic or a similar suitable material
• provide a reasonable degree of protection
Colours
• The two teams must wear colours that distinguish them from each other
and also the referee and the assistant referees
• Each goalkeeper must wear colours that distinguish him from the other
players, the referee and the assistant referees
2. Each team shall have an official and reserve team kit, which shall be declared
on the team colour form. The colours of the reserve team kit (shirt, shorts and
socks) shall be noticeably different from and contrast with the colours of the
official team kit (shirt, shorts and socks). The reserve team kit (including the
goalkeeper’s) must also be taken to every match. Only these colours may be
worn at matches.
Quotes from these two documents.
http://www.fifa.com/mm/document/footbal ... eutral.pdf
http://www.fifa.com/mm/document/tournam ... eutral.pdf