I rarely do anything fancy in terms of background because I know that I will be covering it up - and the picture below shows just how simple it is! Just acrylic paint - the ordinary kind you can buy at hobby stores. In this case I didn't even bother to go right to the edges of the page, because I wanted to do a collaged border.
So because I tend to stay in one colour range I then dragged out my drawer of orange/yellow/ gold/brown elements. Its a very simple technique to create a border in this way and to be honest right now I can't really manage anything more complicated. I don't worry about my collage pieces being the same width, because a varied edge gives it more interest.