since this older topic still lives, I am posting here to let you know we released 2 new versions of Custom-ui that let you use And customize and attribute icon_color.
custom-ui: the most complete version allows for templating to those icon colors. these templates are in JavaScript.
custom-icon-color: only provides that attribute so you can use it in the customize section.
both will allow you to use an attribute icon_color in template: entities, and then use regular Jinja in those templates
there is also support for the entity and button card, and we’ve started working on the Tile-card, but that still needs some work.
while at it, we’ve also released a new plugin:
custom-more-info, developed by @elchininet , and this allows you to control what is displayed on the More info panels of any entity.
(originally in custom-ui to hide the templates it set, but now fully fleshed out to control anything from history and logbook, to any attribute you might want to filter. Or unfilter from HA frontend default filters.)