Question

why isn't: window.setBackground('Black') changing my window background to black ?

Answer 1

does the 'window' match the variable you used in the line to define your window?

I had the problem where I said

win = create the window
window.setBackground

when I needed to do

win.setBackground()

otherwise you might need to lowercase 'black'

Answer 2

Did you create a graphical window first with GraphWin()?

and then do your whateverYouNamedThisWindow.setBackground("black")