You all know what opacity means already right?
'Kay then. Let the tutorial, begin.
And yes, this does not apply to AFF.

If you don't know what opacity means, it means how transparent it is. This does not work on text. It only works on images.

Example: < p style="border-style: solid; border-width: 1px; color: #ff9ca2; background-color: #ff9ca2;"/ >< img src="http://static.tumblr.com/ia0akjm/eANm9v27r/infinite___comeback_logo_by_wonderfuday-d4ye9nc.png" style="width: 200px; height: 113px; opacity: 0.5;"/ >

The largest the opacity number you can insert is 1.0. Setting the opacity to 1.0 means that it has full opacity. The lower the number gets, the lower the opacity the image will have.