Fonts on external display (4k TV) look awful, sub pixel font smoothing gone haywire? I have an LG 42UB820V 4K IPS TV - 3840 x 2160 @ 60hz which I connected via an active mini display port to HDMI converter to use with my Mac Mini (HD4000) at 3840 x 2160 @ 30hz.

Everything works fine and dandy, using SwitchResX to make a custom resolution for 30hz.

The problem is I think OS X mistakenly takes the TV as a YCbCr device instead of RGB, or something along those lines. The fonts look awful, with some text having a kind of inverted halo around them!

Long story short, it actually showed the fonts perfectly at one time and it was beautiful, but after a restart it seems to have reverted to the 'awful' mode again.

How can I fix it now and forever?
I have/had a similar problem with my MacBook Pro and now my newer MBPr with an Asus 27" monitor. I ended up finding a discussion about it and a script in a forum for Dell Monitors.  The script took the monitors EDID information directly and created a display profile for it that overrode what OS X was trying to automatically configure.

Here is the script on github along with a link to the original topic. https://gist.github.com/ejdyksen/8302862

This worked for me to make my fonts readable again on my Asus VE27q.