How to get the text on textmesh rendered opaque?

Take a GUI/3dtext shader. Is there a way to change the background from transparent to opaque in that or make the text background appear opaque?
Or to change the text texture format from Alpha-8 to any other?

Don’t alpha blend. You can use any texture format you want.

Could you reveal a bit more, please? How to set the background color?

You can do whatever you want. Use whatever shader you want.
http://wiki.unity3d.com/index.php?title=3DText