The No1 thing that bothered me with Pharo was its white theme, found it both horrible (yes much worse than Squeak) and very tiresome for my eyes. Even worse was the white theme of Moose which made it impossible or really hard to see scrollbars , for me, so it was also a problem of contrast not just color.
Moving to Dark theme , fundamentally changed my experience with Pharo and made coding much more relaxing. Then I decided to go one step further and implement my own theme, a dark blue theme and add to it a gui tool to allow for full customisation of colors (the theme with the tool are available from configuration Browsers with the name Nireas). Blue is my favorite color afterall, reminds me of sea, relaxing and full of positive energy.
In the end it comes down to what you like and what you find more enjoyable to work with. For me it played a small role that the Dark theme is a new thing with its own set of problem since the change of colors had such a profound effect on my experience with Pharo.