The screen that lets you change the background color wasn't working before. It would let you select and change red, green and blue values, but it never refreshed the screen.
I found that the code writes to location #6000 whenever the value changes. With a change to my driver to update the internal palettes whenever #6000 is updated, I was able to make it work!
I don't have code to load the palettes upon startup with a predefined value yet, but I know the background is saved in memory for when you power off the machine. This is something I will have to add later. For right now, it will boot up with the default background in the color prom.