The most common type of uniform for public schools in the United States is as follows:
"Polo" style shirt, with 2-3 buttons, solid in color (usually white or an approved school color; logo dependent on school district)
"Chino" type pants, shorts, or skirt, usually khaki, black or navy blue in color.
Material requirements of uniforms are varied, though most require no denim. Some districts' restrictions include no leggings or "stretchy" material (unless used as undergarments). Additionally, most school districts do not place restrictions on footwear, other than safety measures (closed toe, closed back, etc).
Some schools additionally prohibit certain colors of clothing, such as black shirts, or even certain types of clothing based on a student's gender. For example, some religious schools require male students to wear pants while female students are required to wear skirts.