This should be easy, and may be a stupid question, but bear with me, it's been a long day.

I need to use the eval statement to execute my function properly. My problem is, the statement is correctly evaluated, but I need to execute what it evaluates. Check out my code below.
Code:
changeWallColor = function(newColor){
     eval("_root.previewWindow.walls."+newColor+".gotoAndPlay(1);")
/////THE ABOVE NEEDS TO EXECUTE, BUT IS ONLY EVALUATED///////
}
Does that make sense? Currently nothing happens when this function is called, but I need it to make a certain MC play, based on what value is passed into this function. Thanks in advance!