It truly is your decision, but your mother is probably doing the right thing.
1. You can NEVER get your TRUE hair color back. It may be close, but not the exact, natural shade.
2. It is so, so, SO damaging to your hair.
3. A color like that can give a bad impression.
4. People might think bad of your mother for letting you dye your hair.
1. It is a good way of expressing yourself.
2. You can pull off a lot of different styles with pink hair.
Balancing it all out, I would say that it is a bad idea. But, at the end of the day, it is your decision. You could always sneak it, i don't know. All that I can say, after that, is you'll get some kind of scolding, once your mother sees it...
Unconditional love is as rare as a child with sincerity.
"For I know the plans I have for you, declares the Lord, plans for welfare and not for evil, to give you a future and a hope." -Jeremiah 29:11 ESV