With the color chooser, you need to make sure you not only select the color from the middle area, but the opacity from the right most slider. On the left you’ll see the two color boxes, the top one is what was, the the bottom is what is.
I just tried on a 4.4.4 device and everything works there too.
I don’t have any 6.0 devices yet. So I can’t test. I expect lots of things to not work with the new permission model.
Maybe try clicking “Reset background to default” and try again?