The Noob's (in)complete guide to CSS for Hubitat

Now that I've got my Virtual Omni Sensor tile showing a text variable working properly, onto the next question.

The tile displays a text list of open contact sensors. If they're all closed the text will simply say "All closed". I'd like to be able to change the tile colour in response to any open sensors and back to normal otherwise. This should be possible (markus looks he did it in post 67) using RM but for the life of me can't figure this out.

EDIT: The bodge I just came out with involves setting the tile background to transparent and simply laying it over a virtual switch tile with no text. However I'd still like to know if anyone is able to set tile colours using RM as this would be a handy trick!