How to get the correct color for window background?

[vib]

I am creating a Popup, Top Window that is Launched from calc.
I am trying to figure out how to get and set the background window color so It matches Calc.
Does anyone know how to do this?

As you can see in the screenshot the menu, text control and buttons pick up everything automatically. The window background color however does not.

[vib]

Sorry, It does pick up theme color automatically. I It was someting had set in the window that had it not working.