Create an instance from the image, tint it and add that in you text! Suppose your image is a MovieClip in the library.
var libraryImage:MovieClip = new LibraryImage();
var cTint:Color = new Color();
cTint.setTint(0xff00ff, .25);
libraryImage.transform.colorTransform = cTint;
op.htmlText = "<p> </p><img src='libraryImage' width='40' height='40' vspace='0' />";
//add empty string at the start and you dont need to concatenate the string.