KColorChooser picks the wrong color when the "Dim Inactive" function is enabled in KDE
The KDE Desktop Effects (in the Focus section) have an option "Dim Inactive" which renders inactive windows more dark. When KColorChooser is used to pick a color, the KColorChooser window is the active window, and the window where the color is to pick from is rendered darker, thus showing the wrong color.
One possible workaround is to implement an optional timer: when "pick color" is used, KColorChooser waits a configurable time (2-3 seconds) to let the user activate the other window, and then let the user pick the color. Gimp has a similar option for taking screenshots.
There is a bug in the Ubutu Launchpad about this: https://bugs.launchpad.net/ubuntu/+source/kdegraphics/+bug/507811 And there it is mentioned that "suspend composing/resume composing" might be another way to solve this issue.