Am I doing something wrong here? (drawRect not showing up)

I’m using this code to try to draw a background (actually, I’m using modified versions of it to
do all sorts of stuff, but w/e, the background isn’t drawing, even when I comment the rest of
the drawing fail out):

var g:Graphics =;
var a:Rectangle = new Rectangle(0, 0, 25, 25); //I use this later in the function
g.drawRect(0, 0, 400, 400);

Am I doing something wrong here? Or is my mistake elsewhere?