Material Properties: Transparency/Set Color as Transparency

Hi

I would like to create a Plane in Mogre und display a picture on it.

Also I like to make the picture transparence by some value
like: Bild1.setTranspareny(value)

And I like to tell the picture this colour (e.g. #ff11a3) specified the transparence area.
like: Bild1.setTransparenceColour("#ff11a3")

It is only possible to use bmp files?

Is there someone with some expierence of the tasks I like to do???