Following the answer and comments by @JohnGB, I spent some time looking for examples of this "almost religious" backlash to changing UI theme colours, and sensitivity to contrast in general. The most recent high-profile example I could find was Visual Studio 11. There are numerous news articles tracking the story, but I'll quote some bits for posterity.
First, the initial beta release reaction:
As part of the recent Visual Studio 11 Beta announcement, Microsoft
released details and images of the newly redesigned user interface
that will be a part of VS11. Presenting a new interface based on a
gray-scale palette that also incorporates a redesign of the familiar
toolbar icons used in previous versions of Visual Studio, the new look
has quickly generated intense controversy. [Feb 2012 source]
Following the initial feedback, another release in May 2012:
Microsoft is breaking out the paints and giving the next Visual Studio
a dash of colour after its drab John Major-inspired beta was branded
hideous, monstrous and depressing by thousands of coders.
The company said it has "increased the 'energy' level of the Visual
Studio 11 themes" in the Visual Studio Release Candidate following "a
lot of actionable feedback" on the beta.
That's corporate speak for saying more than 4,000 coders gave its
Visual Studio beta interface a big, fat thumbs-down for going grey in
Or, as one dev put it: "Going from 2010 to VS 11 Beta, it just hurts
my eyes. Everything looks the same and I have to spend more mental
effort organising where things were on the screen.
Votes were counted on Microsoft's UserVoice poll in April: a month
later the tally stands at more than 7,000. Colour was the single
biggest change request.
In response, director of user experience for Microsoft Developer Tools
Division, Monty Hammontree, says the company has now lightened and
brightened the UI "experience" with bolder theme accents and lighter
background colours. [May 2012 source]
Then, after final release in August 2012:
What do we get? The revamp retains something of the Metro look, and
you can choose between Light or Dark themes. Microsoft has kept the
changes it added following criticism of the preview, with a few
splashes of colour, but the changes are subtle and the IDE still looks
grey and washed out.
Microsoft’s goal was to enable developers to focus more on their code,
but there were few complaints about distracting colours in earlier
versions, whereas the new IDE does tend to make all the icons look the
same. It also seems odd that Microsoft puts so much energy into IDE
design rather than, for example, implementing more of C++11 in Visual
That said, the icon designs are something you soon forget about when
working. [August 2012 source]
Microsoft also released a Colour Theme Editor that allows for more customization on the UI colour front.
Lastly, as to the comment on contrast in general, I stumbled across this site http://contrastrebellion.com/ that also seems very passionate about reducing lots of shades of grey in design, specifically when it comes to rendering content. They provide a selection of links to readability studies, among others, to support their cause.
I found it all very interesting to read, and will look out for more examples going forward.