So, I had Visual Studio 2010 Ultimate, and everything was great.
However, I was confused, thought I wanted MASM, and installed the SDK. This causes strange problems for syntax highlighting. When I'm editing a C/C++ file, for instance, a lot of words (e.g., "data", "add", "sub", "mul", "div", "eax", etc.) are highlighted.
At first, I thought I'd just learn to live with it, but it has gotten annoying.
I could find nothing online, so, I deleted the MASM folder completely (method of uninstallation), uninstalled Visual Studio, and then installed it again.
I fired it up, and the problem persists.