Thanks for the reply! So I've gone down the rabbit hole of adding CSS to change the look of an individual tile, and I'm close but I can't quite nail it.
(The Tile ID I'm working with is 57)
If I do this:
#tile-57 .on {
background-color: blue !important;
}
#tile-57 .off {
background-color: black !important;
}
I get almost the behaviour I want, but the image looks weird:

Now, I read a number of threads, many of which you replied to - I tweaked the CSS a bit, if I do as somebody said in this post:
/* ON /
#tile-57[style="background-color"] {
background-color: blue !important;
}
/* OFF */
#tile-57 {
background-color: black !important;
}
The tile looks fine, but there is no way to reference the on or off state.... it just stays blue regardless of state.
I also cannot figure out the attribute to show a custom icon (even one from the default repository) that I can reference in the CSS? customIcon does not seem to have any effect.