Best practice for conversion between Color Item (HSBType) vs MQTT color xyY thing?

MQTT supports in the latest version the witch color xyY witch is great, since the Tradfri Color bulb using brightness Y and color x, y.
But the color picker item only supports HSB.
There are a lot of transformation scripts from hsb to rgb/xy and they to the work (mostly). But currently, it’s only a HSB > xy conversion. A conversion from xyY to HSB seems nobody to use, but why?
As soon as i set the color, the mqtt broker send the brightness, x, y response which sould be set to the item. E.g. if use a remote control witch send the color red, this color should be shown as well in the item color picker.
Is there anybody who as a solution for this?

My Idea to solve this to unlink the item from the thing and use a rule or nodered to store/update color information the the item and update the color for the thing afterwards.

I am working on the same thing. It is for me not very intuitive.

Widgettype -> Tranformatio? -> Mqtt color type -> Transformation? -> Mqtt command

I saw some Transformations for zigbee2mqtt. I will try to build some thing