Question:
What are requirements for shoes? Are cleats allowed and what colors? I imagine multi colored boots aren’t allowed. But what about a cleat that is predominantly black but has yellow on it. I know I will be wearing my yellow shirt most of the time anyway.

USSF answer (February 27, 2012:
This answer from November 29, 2001 is still valid, although we have updated the content of Advice 5.1:

5.1 REFEREE UNIFORM
Referees may wear only the gold primary jersey or the black, blue, red, or green alternate jerseys, and may wear only the approved socks. (The term “primary jersey” means only that this is the color all referees must have. It does not mean that the gold jersey must be worn in preference to other colors.) No other colors will be worn without express permission of the USSF. If the uniform colors worn by a goalkeeper and the referee or by a team (or both teams) and the referee are similar enough to invite confusion, the goalkeeper or the team(s) must change to different colors. Only if there is no way to resolve the color similarity must the referee (and the assistant referees) wear the colors that conflict least with the players. Referees and assistant referees must wear the same color jerseys and the same style of socks, and all should wear the same length sleeves. The referee uniform does not include a hat, cap, or other head covering, with the sole exception of required religious head covering. Referees must wear the badge of the current registration year. In general, referees, assistant referees, fourth officials, and reserve referees may not wear any item of equipment, clothing, or jewelry (with the exception of a watch) which the Law does not permit a player to wear.

Referee shorts must be black.

Referees should select their shoes with an eye for both utility and appearance. Referees have to run on the field with at least as much speed and agility as do the players, so the shoes should enable them to do this under all field conditions. Players, team officials, and spectators often make initial judgments about the skills and knowledge of the referee based on appearance, and shoes can contribute significantly toward building that reserve of confidence. It is also occasionally important that players, who are frequently looking down at the ground, be able to identify the referee quickly by differences in the shoes. Accordingly, the referee’s shoes should be predominantly black, clean, polished, and neatly tied.

Under normal circumstances, it is not acceptable for a game official to wear headgear, and it would never be seen on a high-level regional, national or international competition. However, there may be rare circumstances in local competitions where head protection or sun visors might sensibly be tolerated for the good of the game, e.g., early morning or late afternoon games with sun in the officials’ line of sight causing vision difficulties; understaffed situations where an official with sensitive skin might be pressed into service for multiple games under strong sunlight, or a referee who wears glasses needing shielding from rain. Sunglasses would be subject to the same considerations. In addition, we ask referees to remember that sunglasses have the unfortunate side effect of suggesting that the referee or assistant referee is severely visually impaired and should not be working the game. They also limit communication between the officials and the players by providing a barrier against eye-to-eye contact. Sunglasses, if worn, should be removed prior to any verbal communication with players.

The Advice does not cover shorts, socks or shoes, but referees who want to get ahead will make every effort to present themselves neatly and professionally. Shorts should be made of the same materials as the jerseys. Shoes must be black and bear as little ornamentation as possible. Referees should dress as conservatively as possible to avoid drawing undue attention to themselves.

The policy on hats was published in the October 1999 issue of Fair Play:

Q. May referees wear caps and sunglasses?
A. With regard to caps, the policy of the United States Soccer Federation was stated in the Spring 1994 issue of Fair Play magazine: “Under normal circumstances, it is not acceptable for a game official to wear headgear, and it would never be seen on a high level regional, national or international competition. However, there may be rare circumstances in local competitions where head protection or sun visors might sensibly be tolerated for the good of the game, e.g. early morning or late afternoon games with sun in the officials’ line of sight causing vision difficulties; understaffed situations where an official with sensitive skin might be pressed into service for multiple games under strong sunlight or a referee who wears glasses needing shielding from rain.” Sunglasses would be subject to the same considerations. In addition, we ask referees to remember that sunglasses have the unfortunate side effect of suggesting that the referee or assistant referee is severely visually impaired and should not be working the game. They also limit communication between the officials and the players by providing a barrier against eye-to-eye contact. Sunglasses, if worn, should be removed prior to any verbal communication with players.