I just installed IDEA 15 EAP (build # IU-142.3926.4) and immediately thought that the UI (both the IDE and the editor panels) looked "faded". Initially I thought that this might be an consequence of using JDK 1.8, but upon further investigation noticed that the "Antialiasing" setting in "Appearance" was "Without LCD rendering".
I changed this to "LCD Rendering in IDE and Editor", applied it and immediately, the appearance was much better, e.g. colors & fonts clearer and more vibrant.
Is there a way that this setting can be made the default for Yosemite? I'm guessing it applies to other versions of OSX but have no way to confirm.