I know you can use a custom CSS style sheet to set two custom text styles in Quixe. But I'm not sure if there's a way to make the background color property show the appropriate custom color in Quixe.
Even if there is, I'm thinking using the text style (rather than using the actual background color property) may be the better way to go to specify a background color for a window, because then one of the styles in the CSS style sheet can be customized to reflect both background color and text color.
On the other hand, defining a named custom style "uses up" one of the two style slots that the story author has available, and so maybe that would be a disadvantage if the author has other text styles they want to use for other things. (Unless the background color property also "uses up" one of the two custom style slots?)