There is font smoothing in addition the ClearType. Briefly, quoting from Disable ClearType everywhere:
Disable ClearType by opening “Control Panel->Fonts->Adjust ClearType text” and unchecking “Turn on ClearType”.
Disable font smoothing by unchecking “Smooth edges of screen fonts” in “Control Panel->System->Advanced system settings -> Performance Settings->Visual Effects.
Change window elements fonts. To do this, open “Control Panel->Personalize->Window Color->Advanced appearance settings” and change all fonts from Segoe UI 9 to any other font.
See the reference above and Disable all font smoothing in Windows 7 (ie: including taskbar, menus, control panel, etc...) for more complete directions, still applicable to Windows 8.1.