Not that I would call this, espeacially on Senior night but just to give a little back up to the guy that called it. I suppose you could back this up with this rule if he considered the different color socks confusing to the apponant.
Rule 3: Players, Substitutes and Equipment
Section 5: Team Member’s Equipment, Apparel
Article 1
Art. 1... The referee shall not permit any team member to wear equipment or apparel which, in his/her judgment, is dangerous or confusing to other players or is not appropriate.
