I've just upgraded Visual Studio and I'm getting this problem, most answers seem to be 'run the installer again and choose repair'. This didn't work for me. Here's what did.
The simple answer for me was to close Visual Studio, delete all .suo files from the solution/project directory and re-open the project. Your Xaml and XML files should now display with colour formatting.
By Luke Alderton at 12 May 2017, 15:50 PM
Tags: Xaml,XML,Visual Studio