Changing CSS variables via JS in Polymer

In my Polymer project i have a toolbar, which's color I want to change using JavaScript. Since Polymer uses the CSS variable --paper-toolbar-background internally for styling, I can't do something like style.color. I found a method named setProperty(), but it doesn't work for me. Has ayone already found a solution?

I would be very pleased if someone could come up with a solution for that, Aaron

via Chebli Mohamed