I removed all of Cinnamon (I suspect) however, even though I explicitly set an image for LightDM to show (it's in /etc/lightdm)
I see it for a second or two, then the old background presents itself.
It appears I missed something, somewhere. Can anyone lend guidance?
While I didn't solve the root cause, I did find that the overriding background was this:
/usr/share/backgrounds/GradientGlowBlue.jpg
Simply renaming this took care of the immediate issue since I only run dwm and this image actually means nothing to me.
I'm marking this resolved ... for now ;)