In KDE 4.9 one can disable the transparency of most items, but not of the Plasma Panel. However, that thing annoys me to all extent. I cannot have applications full-screened then Alt-Tab to another window as the full-screen application bleeds through the panel and I can no longer make out what is actually in the panel (such as reading the clock). Is there any file that transparency depends on that I can simply
Note that turning off all effects is not a solution. I use the effects for some disability issues.