Do you just want a specific color, or the color picker?
There is no direct shortcut that will do it unless you create one with vba.
Shift Ctrl F should bring up the cell formatting box on the font tab, pressing F again should change it to the Fill tab, I haven't used 2003 recently but I'm sure that it works the same as 2007.
The method that Robert suggested might be slightly different, but you should be able to find the correct one easily, just press the Alt key, then navigate the menu using the underscored characters.
