Earlier this week, I installed MonoDevelop 2.0 on my Ubuntu 9.04 system. Having never used MonoDevelop, my first impression was is very positive one. It is one of the most professional-looking applications I have installed on a Linux-based system.
However, I have grown accustomed to writing code against a black background. I expected to find a menu option full of syntax-highlighting options. Alas, there is none! But the solution is easy, once you figure it out...
I eventually found the Syntax Highlighting dialog under Preferences. (Edit > Preferences > Text Editor > Syntax Highlighting).
As you can see, you may can add and remove items from this list. I wanted to make a custom theme, so I found a copy of one of the existing themes and started editing it. I'm not sure where existing theme files are stored locally, so I just grabbed it off the MonoDevelop SVN server, here.
Note: adding themes via the dialog will place a copy the XML configuation file under ~/.config/MonoDevelop/syntaxmodes. These can be edit in place, but if you click "Remove" from that dialog, it'll be gone forever -- so keep a copy somewhere safe, like your home directory.
Here is a maddening little nuance that may save you some time: your theme's filename must end in Style. I wasted a good half-hour finding this out by trial and error. I ultimately called mine RandomlandStyle.xml.
Play around with the XML settings for a while. Most of the node names are pretty self-explanatory. Test it by importing it via the Syntax Highlighting dialog mentioned earier.
An item with your theme's name should show up in the list. If it does not, you may have some sort of syntax error. MonoDevelop may or may not inform you of this. (I had mixed results. You will likely have to restart MonoDevelop if an error occurs.)
The full XML file is available here. (Warning: I'm lazy right now, so it still has leftover definitions from the go-by style I used). Happy coding -- your way!
Screenshot of some fake code I typed out to test a few colored elements.