I was going to show you a render with a picture as a background but for some reason Blender has decided not save renders today, anyway, if you go to the output screen, the left screen on the bottom, you will find an open file icon beside backbuff, click on that and your "work area" will fill with a screen that will alow you to select a picture for the background on your render, if you want a solid color I guess you could find a picture of a blank screen the color you want. When you have your picyure selected click on the button in the upper right corner that says select backbuf, then click on the button in the output screen named backbuf to activate it and you will have a backdrop in your render. You can also in the render screen select sky for you backdrop, it is by default a darkish blue background.