When I select a window from the taskbar, the opacity for the window changes accordingly with what windows I select.

How can I change the opacity level for the window?
I cant find where are the settings for it in KDe 4.4.4

systemsettings>Desktop>DesktopEffects>AllEffects(tab)>Translucency is not the solution. It doesnt set the transparenncy for those windows...

There is no option to change the level of opacity. It's only possible to disable the highlighting in task manager's settings - called "Highlight windows"