I just upgraded from a 2011 MacBook Air to a new Retina MacBook Pro, and I use an external display (Acer K272HUL, via a Mini DisplayPort -> DisplayPort cable).
All text on the new display (everything from webpages, to native app content, to the OSX menu bar) now has this strange "haloed" effect, in which text is surrounded by white pixels. It's not a solid outline, but just enough "glow" to be distracting.
I've included a screenshot of the effect below, but I'm not sure how useful this is. The image looks bad when I view it on my external display, and normal when I view it on the Retina display. (Though it's interesting to note that whatever's going on affects images as well as rendered text.)
I might have attributed this to the difference between Retina and non-Retina screens... except that this doesn't happen when the external display is plugged into my old MacBook Air.
Does anyone know what's going on? I found another question that seems to be related, but it didn't have much detail or any answer activity.