If you are at junior high or high school, perhaps you are trying to find out who you really are and desire to try different styles and looks. However, your school perhaps have rules against a number of things, such as hair colouring.
Lots of public and private schools ban distracting colours like green, pink, and blue. Students who disobey the school rules can be give suspension.
Rather than wishing for a change in the school policy, working with the regulations and changing your hair tone drastically in certain ways which will not get you in trouble is a great idea.
First off, why not trying the bottom layer? If you are really eager to dye your hair a bold tone which your colours will not grant, you can consider dying just the bottom layer if you have quite long hair.
You can simply hide the change by wearing the hair down and then pull it up when the school official are not around and during the weekends to show your friends your bold hair tone definition.
Next, you can try the koolaid. If you just want to challenge the school officials and show up with an overt bright green tone on your hair, you can consider using the powdered drink mixes rather than standard hair dye.
If your teachers send you home or even threaten a suspension, just wash your hair and the dye will be gone. The other bonus to using this trick is that you can get colour change frequently.