About the background layer

When you create a new image with a white background or a colored background, the bottommost image in the Layers palette is called Background. You cannot change the stacking order of a background, change its blending mode, or change its opacity. However, you can convert a background to a regular layer. (See Adding layers.)

When you create a new image with transparent contents, the bottommost layer is called Layer 1. This layer is not constrained like the background layer; you can move it anywhere in the Layers palette, and change its opacity and blending mode.

Because the background can never be transparent, it's helpful to have a background when you want to create an image that will not have any transparent regions. If you want to create an image with transparent regions--for example, for a transparent GIF on a Web page--you'll want to create an image without a background. For information on converting a layer to a background, see Adding layers.

Using Layers > Using the Layers palette > About the background layer