I've written a class method I use to configure new images.  I'd like to have
the method set the desktop set to black, but I can't figure out how to do
that.  I've looked at the changeColorTarget message in Morph, but after that I
get lost in the ColorPickerMorph (which I'm guessing is unnecessary because the
color's already picked).  What is the code needed to set the desktop to black?