Card color based on a state attribute?

I have a couple of RGBW lights that present themselves as two entities, one white, the other RGB. I’m trying to expose them in the dashboard as a single Tile card with a brightless slider and the RGB light setting the card color (the color itself is being set by an automation, I’d just like the UI to show the current color setting). However, since dashboard card configs aren’t templates, this doesn’t work. Is there another path?

type: tile
entity: light.rgbw_light
name: RGBW lightstrip
features:
  - type: light-brightness
color: rgb{{ state_attr('light.rgbw_light_2','rgb_color') }}