Not much of a how to in the info of that node. I did not see any links to more documentation.
Try using the change node to create the msg, and use msg in the data input field.
e.g.
[{"id":"187967a.a95e618","type":"inject","z":"4484ee28.caa3c","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[255, 0 , 1]","payloadType":"json","x":150,"y":500,"wires":[["67f3f52c.e2114c"]]},{"id":"67f3f52c.e2114c","type":"change","z":"4484ee28.caa3c","name":"","rules":[{"t":"set","p":"hold","pt":"msg","to":"payload","tot":"msg"},{"t":"set","p":"payload","pt":"msg","to":"{\"brightness\":\"35\",\"effect\":\"None\"}","tot":"json"},{"t":"set","p":"payload.rgb_color","pt":"msg","to":"hold","tot":"msg"},{"t":"delete","p":"hold","pt":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":350,"y":500,"wires":[["269a25ff.79887a"]]},{"id":"269a25ff.79887a","type":"debug","z":"4484ee28.caa3c","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":590,"y":360,"wires":[]}]