What to do about dark roots??

I have dark brown hair and would like to do more of a all over honey blonde highlight look. The only thing that is holding me back is the thought of dark roots! Is there a way (at the salon) that the stylist can just touch up your roots every few weeks? How often do you need to get your roots done? Thank you!

My hair is naturally some kind of brownish dark blonde and I had mine dyed platinum. I did my roots every 3 weeks and no one ever really noticed them. I knew a girl with black hair who went platinum and she had to have hers done every 2 weeks (this is just to be sure no one ever saw them, if you didn't worry about it and let it go a little, you could wait longer).