ActionScript for Flash MX: The Definitive Guide, 2nd Edition By Colin Moock
Chapter 18. ActionScript Language Reference
TextField._alpha Property
Flash 6
opacity percentage: 0 is transparent; 100 is opaque
read/write
theField._alpha
Description
The floating-point _alpha property specifies the opacity (or, conversely, the transparency) of theField as a percentage 0 is completely transparent, whereas 100 is completely opaque. The text, background, and border of theField are all affected. The _alpha property works only when theField's font is embedded and exported with the movie. A font can be embedded at authoring time with the Property inspector's Character button or at runtime with the embedFonts property. For important details on font embedding, see TextField.embedFonts.
Example
Assuming its font has been exported with the movie, the following code makes theField_txt 50% transparent:
