Microsoft has added the ability to change the active “button set” to a couple of alternatives, in Windows 7 logon UI. This setting can be used to improve text readability with lighter or darker backgrounds, as the case may be.

To do so, open Regedit and navigate to

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI

Add a DWORD value named ButtonSet.

The supported integer values range from 0 to 2, with each value defined below.

0 – Lighter text shadows, darker buttons (Default)
1 – Darker text shadows, lighter buttons (for lighter backgrounds)
2 – No text shadows, opaque buttons (for darker backgrounds)

Thanks: WithinWindows.