The issue with gray uniforms, for players or referees, is sweating. Years ago, I was doing Sunderland v Portland (exhibition match). Sunderland, of course, was wearing black and Portland was planning to wear forest green. Ah, no. As the players sweat, those forest green shirts become almost black. Portland agreed to wear white. As referees or players sweat, those gray uniforms get dark. By requiring a darker grey to start with, the high school player shirts can't be worn as "white."