To make a background transparent, just do android:background="@android:color/transparent".
However, your problem seems to be a bit deeper, as you’re using selectors in a really weird way. The way you’re using it seems wrong, although if it actually works, you should be putting the background image in the style as an <item/>.
Take a closer look at how styles are used in the Android source. While they don’t change the text styling upon clicking buttons, there are a lot of good ideas on how to accomplish your goals there.