Version 4.20a (Win x64) of Segger's Embedded Studio has problems with it's C syntax highlighting -- specifically conditional compiled sections of code. Code that is not being compiled is supposed to be greyed out; however, some sections of code that are compiled are also greyed out.
Not a big issue unless you are trying to figure out how the code works and rely on the syntax coloring to provide clues as to what options are set and not set in the various configuration files.
As an example I have a proj.conf file that has the CONFIG_USE_UI_MODULE definition set but code that is dependent on this definition is marked as not being compiled although placing a #error pre-processor statement caused the compile to fail, thus indicating the code was being compiled.
If you are trying to figure out how the various config options work, be careful of trusting the highlighting. And also remember that the prj.conf file is only read when SES opens the solution so close and re-open the solution if you make prj.conf changes.
