How to specify color values for Hue bulbs?

I have some Hue bulbs in HA that I control with a Conbee II. I am trying to set up an automation and under the light:turn on service I want to specify the color either by RGB, Hue/Saturation or X/Y but none of them work, the only parameter that works is Color Name.
Any suggestions?
Thanks.

There should be an attribute named ‘supported_color_modes’, enumerating the … well … supported color modes.