You can adjust the color by right clicking on your desktop and clicking "personalize". You must have the proper graphics card and drivers to ensure that Windows Aero will work.
Generally, Windows 7 is faster than Windows Vista. This is partly through a process of analysis of code to look for bottlenecks between Vista and 7 and improved memory management of screen Windows in...
Windows XP uses less RAM (Random Access Memory) making it "faster". However, if your computer has a good amount of RAM Windows 7 will work just as well if not better.