I have an IKEA KAJPLATS_WS bulb
Features via Zigbee through Gladys gateway
ON/OFF - Brightness - Light temperature - RGB
Features via Matter through Gladys gateway
ON/OFF - Brightness
Why do I lose the light temperature setting and the RGB setting with the Gladys Matter integration?
(Features via Matter through IKEA DIRIGERA gateway
ON/OFF - Brightness - Light temperature - RGB)
Hello @Chris75,
Thanks for reporting this. This is a current limitation of Gladys’ Matter integration, not the bulb or Matter itself.
When connected directly, the bulb exposes the color via the Matter modes XY and ColorTemperature. However, Gladys currently only handles the Hue/Saturation mode of the ColorControl cluster in Matter.
The ON/OFF functions and brightness are therefore recognized, but not yet the temperature or color.
Zigbee2MQTT and the DIRIGERA gateway correctly translate these capabilities, which explains the difference.
We will need to add support for ColorTemperature and XY in Gladys. Could you create a feature request here: Demande de fonctionnalités - Gladys Assistant community
Thanks! 
ok, but for my information, I’d like to know if this kind of feature can be handled by an external integration or if it necessarily requires a modification of Gladys’ core?
And can we develop this with Node-RED?
For now, Matter integration is intended to remain at the core of Gladys, as it is a truly major integration.
However, if someone wants to develop a competing Matter implementation as an external integration, nothing prevents them from doing so. That is precisely the interest of this new architecture: everyone is free to experiment, innovate, and propose their own approach. 
Yes, absolutely! There are Matter packages for Node-RED, so it is a perfectly feasible option.