TextField alpha

In the help-files it clearly states that it is possible to change the _alpha of a created textfield. But trying with the following code wont get the job done:

[AS]
// step 1) Create textfield
createTextField(“myText”, 1, 100, 100, 100, 100);

// step 2) Set some values
myText.border = true;
myText.background = true;

// step 3) Add the text
myText.text = “Dude, wheres my joint”;

// step 4) TRY DOING ALPHA - (does nothing, though)
myText._alpha = 50;
[/AS]

The code should be fine according to the help-files, so what am I doing wrong?

Thanks