Background Color for Dock Widget, App Switcher,…

I would love to be able to set a background color to these widgets. It allows me to better "delimit" visually the elements, and at the same time attracts less the regard than a black space. Look here the messages icon (first as the item fron the dock widget, then as a personal script).

Next super nice thing would be to be able to ignore the running status (white dot) below the app and adjust the apps size :innocent:

Unlinked question: how do you extract the information of the dock, especially the icons? I know that my request could be too specific to match many users, so knowing this might just allow me to construct my own workaround.