@tomcoleman according to this post, below code should be the correct (and shorter) code to change the color. I tried it myself and indeed changes the state color to red, so you should use this code now.
card_mod:
style: |
ha-card .states.flex {
color: red;
}
Why my template doesn’t work I don’t know (tested myself and indeed doesn’t work). Use the search button in the card-mod thread and look for templates, so you can use above code in a template example.