Toggle stack color

I know this can be done.
I just don't know right now how to do it. 

How do I set a stack's background color to change when it is open/closed?

Well this is a bummer.
I found a stickie/stack to use as a model (FFF_Tea_1).
It has a stack that changes color when opened/closed.

I created two vertical bars, the same as in the model.
But when I ran my stickie/stack the color didn't change when opened. 

Figured it out.