Hmmm...well use this:

Now the BG color can't be done with the as3 textarea, you'd have to extend the class or skin it in the library to change the bg color.

Code:
import fl.controls.TextArea;
var ta:TextArea = new TextArea();
var textAreaFormat:TextFormat = new TextFormat();
textAreaFormat.font = "Arial";
textAreaFormat.size = 12;
textAreaFormat.color = 0x0000FF
textAreaFormat.bold = true;
ta.setStyle("textFormat", textAreaFormat);
ta.htmlText = "The quick red fox jumped over the lazy brown dog.";
addChild(ta);