This tutorial shows how to change the usplash which is a flash screen after typing user and password in login window.
Step1: Install an GUI tool:startup-manager
sudo apt-get install startupmanager
Step2:Launch startup-manager from System->Administration menu.Select Appearances tab and click on Manager usplash themes,then choose your favourite theme.
You can also click add to add more themes,download theme from :http://www.gnome-look.org