How to remove transparency in KDE without disabling all desktop effects?

Go to: System Settings->Desktop Effects->All Effects and scroll down to "Translucency" or search from the search bar which is there and just disable it and hit Apply. - that's for disabling Opacity while u move the window.

If your window is transparent even if u don't move it, just press Alt+F3 on the selected window and go to: Opacity->100%

Q:

"...but my problem is not to disable transparent windows, but panels, widgets, notifications, tooltip-previews, menues and stuff..."

A:

Earlier: How to change color/transparency of all desktop panels?

Here's an opaque theme: Big-Blue

I just installed it and it has removed transparency from the "task manager" bar. Legibility recovered!!!
--->

( To install for KDE 4.13: go to: System Settings--> "Desktop Theme" ; click "Get New Themes..."; type 'Big Blue' into the search box; click install; close the dialogue; select that theme; click apply. Yeah! )