On Windows 8, you can easily personalize the lock screen image, system color scheme and the Start Screen background from PC settings, but Microsoft has not provided an option to customize the logon screen background colors. Logon screen (seen below) is the interface where all user accounts are displayed. If you’d like to change its background color, then it can be done from the registry, and here’s how.
Change Logon Screen Background Color
Open Registry Editor (Run > regedit), and navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Accent. If you cannot find the Accent key under Explorer, create one. Then select Accent key, right-click in the right-pane and create a new DWORD (32-bit) value called DefaultColorSet.
Pick a color scheme you like from this chart and note the corresponding decimal value:
Now either right-click on DefaultColorSet and select Modify or double-click on it to change its value. Switch the base to Decimal in the edit dialog and enter in the value you chose from the above chart.
That’s it. Log off now to see the changes. If you can’t see it immediately, restart your computer.