ASH: ActionScript Source Code Highlighter (Beta 2)
ASH is still has a way to go, but you can test it out below.
// place your code here this.createEmptyMovieClip("sample", 0); with (this.sample) { lineStyle(1, 0xFF0000, 100); beginFill(0xFFFFFF); lineTo(100, 0); lineTo(100, 200); lineTo(0, 200); lineTo(0, 0); endFill(); }