I have same bulb. It’s also possible to control color using HSB.
{"brightness":254,"color":{"hue":42,"saturation":80,"x":0.512264,"y":0.438988},... is sample input of your device. hue_value, saturation_value, brightness_value/2.54 are your HSB values.
You may set coloritem state hue_value, saturation_value, brightness_value, as {“brightness”:brightness_value,“color”:{“hue_value”:42,“saturation”:saturation_value}}.
Please note, that color and brightness are operated separately. At first brightness is changed, secondly color is changed. Device reports both states. Therefore you should debounce input by 200 msec.
For parsing note Zigbee2mqtt revisited: No more ugly transformations
