You may run across a server that is blacked out on the login screen. You can still login but it makes it difficult finding the username or password fields.
To fix this you should look in the registry at:
HKEY_USERS\.DEFAULT\Control Panel\Colors
You will probably notice that all the values or almost all the values have zeros in them. You need to replace these from another server. You can replace these with the values listed below if you don’t mind the colors. Just save the values to a .reg file and import them back in: