SETTING BACKGROUND COLOR IN PHOTOSHOP

You have the option of setting the background color on a Photoshop file when you first create a new file.

When you go to FILE/NEW there is an option to set the background content - to white, background color or transparency. In most cases you will want to choose transparency. PS will "remember" this setting for the files opened after that.

Also, if you need to delete a background color, once you have opened a file you can just select it (apple/a) and cut the object out of the layer.