iam too too sure what you mean? is it that you want to change the background color from the default gray into i.e. blue. go to window > settings prefferences > colors...
there are 3 menus. general, active and inactive. in the general tab go through the options. you should come to "background". then ajust the color that you want.

i think the problem is that you hit the 7 key. this displays how much light you have in your scene. so your work area turned black because you have no lights. press 5 or something to change back to normal.

hope that helped.