Sorry for the delayed response, been out on vacation.
In this instance, I added the script to the Project Library, I named the script testScript
Then on a label, I added a custom property sate. I chose to use the backgroundColor attribute of the style to select the base color, though you could also create a custom property for this. Using the backgroundColor allows you to use the color picker.
Then I added a binding to the backgroundImage style attribute with the following expression:
The following is the result:
