In the screenshot you shared, the day name row is all the same color, but you're wanting to be able to change just the color of the name and have a background color for the days of Saturday and Sunday?
Currently there is an option to change the color for Saturday and Sunday dates, but the row of the day names remains in the base color of the widget.
I see now. I was thinking you meant to only change the day name color of Saturday and Sunday.
so instead of the text color of Saturday and Sunday being different from the rest, you want to be able to have it shaded in the background, right? If I implement this way, I would have to force it to disable the highlighting of dates based on completed reminders, but I'm betting that would be okay for you, right?