You can actually use the ICSharpCode.TextEditor bundled with the Sharp Develop IDE source code. This is a fully-featured code editor. Using that control you can define your own syntax color rules and auto complete lookups.
Install the nuget package:
PM> Install-Package ICSharpCode.TextEditor
A good tutorial is available at http://www.codeproject.com/Articles/30936/Using-ICSharpCode-TextEditor
