There are many apps, tweaks and command line code to customize your Mac. Some are not for the faint of heart when it comes to using the Terminal in OS X. Terminal tweaks need to be typed in exactly or they either will not work or could damage your OS (if using a SUDO command). So unless your experienced with Terminal you should steer clear of this method. Apps are best way to go when it comes to more novice users and Lion Designer 2 (V 2.9.9) would be a safer route to use.
What this little Gem does is give you a pretty straight forward UI to change Mission control, Dashboard, Login screen backgrounds. It will also change the icons for Launch pad folder, Login screen icon and FaceTime ringtones. LD 2 has a setting to change the Finder icons on the left of the window to colored icons (opposed to the grayed out stock icons) you can also hide your desktop icons and user library. It has drag and drop functionality and with the click of a button you can set it all back to default incase you don’t like what you changed. It also has a very handy conversion window so you can convert images to the proper size before setting them. Lion Designer 3 Beta will be out in the near future and hopefully with some added tweaks. If you want to use this app you need to have an Intel based Mac 64 bit and be on OS X 10.7 or higher.