At that time the visual designers were strongly urging that all icons be greyscale because they said color was "distracting". I overruled them and insisted the icons have color because it was better for overall usability.
Now the whole industry seems to have come under the influence of the visual designers favoring visual appearance over usability. Much less attention seems to being given to real overall usability.
And then they ripped the text labels out of the Windows taskbar, as if we are supposed to remember what the icon for Word and Outlook looks like today.
I honestly don't know how the most loathed form of support, phone support, can even do it these days.
Did they run labs with actual users to check how they reacted to the monochrome icons?
If you do that well, you can use color to convey another dimension, much like it layers meaning on top of source code (by coloring keywords, variables, comments, etc)
http://blogs.msdn.com/b/visualstudio/archive/2012/02/23/intr... (the hilarious original annoucement)
https://www.hanselman.com/blog/ChangeConsideredHarmfulTheNew... (commentary)
https://visualstudio.uservoice.com/forums/121579-visual-stud... (a rollback)
https://docs.microsoft.com/en-us/visualstudio/extensibility/... (Visual Studio 2017 icon color pallette and guidelines)
It's unbelievable it was even implemented, let alone released.
I don't buy into it, though. They tried monochrome grey icons in Visual Studio 2012, and people hated it, for good reasons. So now VS icons have colors again.