Bright colors...don't want to lose my natural color?

Okay, here's the deal. For the longest time, I've wanted to dye my hair some kind of bright or outrageous color, but my parents have been completely against it, because they "Don't want me to lose my natural color". My hair's naturally a reddish chestunut brown, and is very long (waistlength), incredibly thick, and has never sen a perm, dye, or any other kind of drastic measure. I've been told by...well...practically everyone I've met that if I dye my hair, it will never grow back exactly the same. And I know that most bright-color dyes don't work well on brunettes unless you bleach your hair (Which I really don't want to do). The only other alterniative I can find is henna, but I also know that might turn it orange instead.

So, any suggestions as to a dye that's more gentle on the color you've got?