For some reason after the Yosemite installation when I tried to change the Display Settings to "Best for Display" resolution font smoothing just went crazy. I tried to do the following without any effect.
- Forcing RGB mode - I did the workaround suggested by the author (taken from a commenter)
- Changing Font Smoothing Settings in Yosemite
The workaround involves creating a new user and re-logging in to that new user. I know this is painful but for me this is a quick workaround because the old user is disposable for me. In the new user I notice that the Display Settings resolution is scaled but it does not indicate which scale it used. The BIG NOTE is not to use auto-scale resolution this time in the new user.