It is indeed worded in a strange manner. I can think about 2 idioms: - "to be green" = to be immature / untrained / inexperienced or to be concerned aout the environment - "to be in green" = to wear green clothes But I never met the expression "to be in the green" to be honest.

This is a very awkwardly phrased sentence. It should be "the female student is in the green". It means she is wearing green.