Clemens,

on Windows, the RubyWin IDE also uses Scintilla as its editing component,
and the TODO list mentions syntax coloring. It may ne worth checking with
the author Masaki Suketa if he has taken any steps towards this.

see:
http://www.ruby-lang.org/en/raa-list.rhtml?name=RubyWin

Good luck and t.i.a,

Bernard.

FYI, Mark Hammond's PythonWin IDE also uses Scintilla, to a very
convincing effect...