VAX provides the functionality to display source comments for C++ files. This is indeed a nice feature and I have noticed that some keywords like "\\brief" are marked as bold. But XML comments a written in plain text. Is there any possibility to color or highlight XML comment like coloring in code editor?
Unfortunately, there is no option to do that. Which IDE version and programming language are you using? You mentioned C++, but Visual Studio is not coloring <summary> and <remarks> in the code editor to grey for me. Not even with C++/CLI (Windows Forms Application project) On the other hand, in C#, where the coloring is like on your screenshot, VS2008, VS2010 and VS2012 only shows the summary of the comments in the tooltip (with VA).
We use Visual Studio 2010 Professional Version 10.0.40219.1 SP1Rel with C++/CLI. The tag coloring can be configured in "Fonts and Colors" with "XML Doc Tag" entry.
In XML comments there can be tags inside tags. For example <see cref="OtherClass" />. Maybe these words can be printed bold. But I think your developers will find a nice and clean way for displaying XML comments. ;-)