Amendments to the Laws of the Game
Law 4: The Players Equipment Present
USSF Advice to Referees: The general purpose of this change is to ensure that the visible color of any portion of a garment worn underneath the jersey or shorts is consistent with the main color of the jersey or shorts. Accordingly, the referee need not be concerned about the color or any portion of an undergarment which cannot be seen.
New Text
•a jersey or shirt – if undergarments are worn, the color of the sleeve should be the same main color as the sleeve of the jersey or shirt.
•shorts – if undershorts are worn, they are of the same main color as the shorts.