Well, Sindea, I didn't know that you could define a bg color when you first create your LO.

But there are several things you can change the background down the road. If it's just a straight color, you could use the paint bucket tool to change the color of the whole layer. Or if you're not 100% sure that you want to get rid of your background, create a new layer with whatever pattern or color you want. Place the new layer above the background in your layers palette and then by turning on and off the new layer you can see your LO with either bg.
To change the transperency of a layer, just adjust the "opacity" slider in the layers palette.
HTH!