Visitors wear gray.
 

NFHS. Home wears white. Visitors wearing a light gray.
Visitor school colors are red and white.
Legal?

Rule says a "contrasting dark color" for the visitors. I'm not an expert on colors, but, especially for the purpose at hand, light gray is neither dark nor contrasting.

From 2011-12 Rules Changes...
 

A new note was added
recommending that the visiting
team’s dark jersey be the darker of
the school’s color scheme or black.
 Light blue, light gold and light silver
visiting uniforms continue to be
problematic since they are difficult
to differentiate from the home white
jerseys.

Not made illegal, just guidance away from getting new ones I guess. Kinda like the division line and center circle being properly marked.