A client of mine had an issue of the 2003 SBS Server’s logon screen having black fields. The user name, password and domain fields were black and you could not see what you were typing unless you ran your mouse over the field to highlight it.
I found a Microsoft article that describes an easy fix. Go to another 2003 SBS Server and export the HKEY_USERS.DefaultControl PanelColors key, save it and then import into the server that has the black logon problem.
The core issue is that the color key has several fields that are color coded with 0 0 0 wiich indicates black and this import sets it back to defaults.