How to Change Color and Transparency of Tabbed Docks?

Right click on the tabbed dock and select settings. You will see Style/Color. Select Enable tab coloring then select a tab name and choose a standard color or choose a custom color.

You can't change the transparency in the settings. What you can do is find the background .png in the ObjectDock folder. Bring it into a graphics program and adjust the transparency there.

What he said.