Have had some problems with Visual Studio 2017 and my color scheme (self created). But at every startup VS changed the color scheme to something completely different. No other settings where affected only the colors were changed. This bug have now been fixed in the latest update to VS.
You can follow the thread at:
https://developercommunity.visualstudio.com/content/problem/44258/visual-studio-2017-randomly-changing-font-colors.html