There is a custom syntax color theme maker for Visual Studio here: http://studiostyl.es/schemes/create. Its user interface is pretty close to what you’re describing. And there might be some way to convert Visual Studio color themes for use with other editors.

However, that page is not very good for creating dark-background themes. It’s missing a bunch of styles that I saw fairly often in C# code, and their default light colors look awful on a dark background.