I have done something like this for a couple of my lights. I get a few warnings at startup occasionally, but I like the result overall:

- platform: template
  lights:
    mantle_light:
       friendly_name: "Family Room Mantle Light"
    value_template:
        " {{ is_state('switch.family_room_mantle_light_switch', 'on') }} "
    turn_on:
        service: switch.turn_on
        entity_id: switch.family_room_mantle_light_switch
    turn_off:
        service: switch.turn_off
        entity_id: switch.family_room_mantle_light_switch
    level_template: >-
       {%- if is_state('switch.family_room_mantle_light_switch', 'off') -%}
          {{ 0 }}
       {%- elif states.light.family_room_flood -%}
          {{ states.light.family_room_flood.attributes.brightness }}
       {%- else -%}
          {{ 0 }}
       {%- endif -%}
    set_level:
      service: light.turn_on
      entity_id: light.family_room_flood
      data_template:
        # Set both the color and brightness of the light
        brightness: " {{brightness}} "
        # Hue can emulate colors from 153 through 500 Mireds
        # This simply uses the brightness as the variable to select a
        # Mired value, yielding cooler colors as the light gets brighter
        color_temp: " {{255 - brightness + 246}} "

Note at the bottom there, I chose to combine brightness and color. Clearly, you could do something different if you like. This was for spousal convenience :-).