I think it is right --- a high school student to wear a clea

填 for .
right 这个形容词是用来说明 to wear a clean and plain hair这件事的.即：To wear a clean and plain hair is right .这时用for .
如果形容词是用来说人的,就用of ,例如：It's kind of you to help me.
即：You are kind .而不是 To help me is kind.