Just to b clear, I am talking about method handleCommand in thing handlers that should accept a value in Kelvin o mirek.
Basic UI sends a value like "4000 K" so it should be supported by bindings, even those working with mirek internally.

AmazonEchoControl => Not Ok

AVMFritz => Ok

Bluetooth => TBD

TBD

Dali => Ok

Deconz = Not Ok

Govee => See #17812

Hue => Ok (albeit bad code)

Lifx => Ok

NanoLeaf => Ok

TapoControl => Not Ok

TpLinkSmartHome => Not Ok

Wiz => Ok

MQTT::EspMilight => Ok

I think Tradfri doesn't support that as well. Here's a device:

(It says "Thing type: Colortemperature Bulb (white)")

And here are all channels, brightness and color are Dimmer:

Zigbee => Ok

https://github.com/openhab/org.openhab.binding.zigbee/blob/d76053983c7ecef170503372763d6dbdcc252eb2/org.openhab.binding.zigbee/src/main/java/org/openhab/binding/zigbee/internal/converter/ZigBeeConverterColorTempAbsolute.java#L57

I think Tradfri doesn't support that as well.

Right, but this issue is about a different topic: it's not about absolute color temperature not being supported, it's about absolute color temperature commands potentially not being handled correctly if supported.

Is this the reason why I receive an error "type" 2 since I switched to openHAB 4.3?

I just updated to 4.3 and since then I cannot change the color temperature of my deconz bound lights.
Logs say:
2024-12-18 13:21:03.115 [WARN ] [ernal.handler.DeconzBaseThingHandler] - Sending command 4000 °C to channel deconz:colortemperaturelight:raspi4:Deckenlampe_Hobbyraum_Mitte:color_temperature failed: 400 - [{"error":{"address":"/lights/2/state","description":"body contains invalid JSON","type":2}}]

Thing:

Bridge deconz:deconz:raspi4 [ host="<ip>", httpPort="8090", apikey="<key>", port="4431" ] {
        colortemperaturelight   Deckenlampe_Hobbyraum_Mitte                             "Deckenlampe Hobbyraum Mitte"           @ "Hobbyraum"   [ id="2" ]
}

Item:

Number:Temperature          Deckenlampe_Hobbyraum_Farbtemperatur
                "Farbtemperatur Deckenlampen Hobbyraum"
                <colorpicker>
                (Deckenlampen_Hobbyraum, Lampen_Farbtemperatur)
                ["Control", "ColorTemperature"]
                {
                    stateDescription=" "[
                            min="250",
                            max="454",
                            step="1"
                        ],
                    unit="mired",
                    homekit="Lighting.ColorTemperature" [minValue=250, maxValue=454],
                    nightshift= " " [startzeit="21:00"],
                    channel ="deconz:colortemperaturelight:raspi4:Deckenlampe_Hobbyraum_Buecherregal:color_temperature" [ profile="ruby:mired_to_kelvin" ],
                    channel ="deconz:colortemperaturelight:raspi4:Deckenlampe_Hobbyraum_Mitte:color_temperature" [ profile="ruby:mired_to_kelvin" ],
                    channel ="deconz:colortemperaturelight:raspi4:Deckenlampe_Hobbyraum_Schreibtisch:color_temperature" [ profile="ruby:mired_to_kelvin" ],
                    farbtemperatur=" " [
                            tageslicht=250
                        ]
                }

According to Error handling - deCONZ REST-API error "2" means "This will be returned if the JSON in the body couldn't be parsed."

No idea what I should do with it. 😳
Any recommendations?

Is this the reason why I receive an error

Yes unfortunately that is indeed the case. We were "too fast" in improving the OH functionality.

It will in particular occur when you try to command the color temperature via the new Colortemperature picker control.

There is a fix in #17919 which will certainly appear in OH 5.0 and probably hopefully back ported into OH 4.3. @lolodomo ??

In the meantime, the work around for you is to command the channel from an item of type 'Number' rather than one of type 'Number:Temperature' (or from within rules send a plain number value e.g. 4000 rather than 4000 K.

This issue has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/openhab-4-3-zigbee2mqtt-color-temperature-in-mired-not-working/160911/4

First of all thanks for the reply. In this case I went back to 4.2 as Number typed items also throw the same error both on UI and via my JRuby defined rules.

This issue has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/openhab-4-3-milestone-discussion/158139/115