How to get just part of a variable

I have a movie that is passing the name of a movie clip to the _root. The problem is I can only get it to pass the entire name including the path by using this:

blueButton.onRelease = function() {
trace(this._parent);
}

it returns this:

_level0.scrollPane.spContentHolder.blue1

**I would like to have it return this: **
blue1 or even just 1

How can I do this?