PLAYER UNDERGARMENTS (AGAIN)

Question:
Most youth teams do not have long-sleeved shirts or thermal underwear as part of their team uniform. Instead, it has been customary in cold weather for players to wear their own long-sleeve shirts or thermal wear under their jerseys. More often than not, these undergarments do not match the players’ jerseys. Now that the new “matching undergarments” rule has been adopted by FIFA, in cold weather games should a referee (i) enforce the rule and thus require the youth players to either remove their mismatching undergarments (risking hypothermia) or not play or (ii) follow the guidance of the USSF’s position papers on the “no sleeves” rule and exercise common sense and judgment, not enforce the rule, and allow the players to play with the mismatching undergarments?

A leading question to be sure, but one that could use official guidance from the USSF.

USSF answer (April 10, 2008):
Even with the recent IFAB interpretation regarding the color of all undergarments, this answer of November 14, 2002, still applies. Please note that we have updated the excerpt from Advice to the current edition:

Under normal conditions, players are restricted to the uniform and equipment specified in the Laws of the Game under Law 4: jersey or shirt, shorts, stockings, shinguards, and footwear. This and other pertinent information is encapsulated in section 4.1 of the USSF publication “Advice to Referees on the Laws of the Game”:

QUOTE ADVICE
4.1 WEARING UNIFORMS
It is implicit in the Law that each side wear a distinctively colored jersey, that shorts and socks be uniform for each team, and that the uniforms be distinguishable from the uniforms worn by the other team. However, the details of the uniform are governed by the competition authority and can vary widely from one match to another. The referee must know and enforce the rules of each competition worked. Players’ jerseys must remain tucked inside their shorts, socks must remain pulled up, and each player must wear shinguards under the socks. All undergarments (slide pants, undershirts, etc.) which extend visibly beyond the required uniform must be as close as possible in color to the main color of the uniform part under which they are worn.
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END OF QUOTE FROM ADVICE

However, the intelligent referee will try to make an exception due to severe weather conditions, such as knit caps or gloves on very cold days. This would even extend to tracksuit pants, provided everyone on the team wears the same color — which need not be the same as the color of the shorts.
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Furthermore, it is not uncommon for local leagues (less so tournaments) to have a local rule exception dealing with less than perfect uniforms.