Assuming you send a message from a function node, to a knx-ultimate node with Group Address and Datapoint properties set.

To colorize a lamp that support colors, like Philips HUE, you can pass the colors in red, green and blue values.
Create a function node and paste this code.

Set RGB color, Datpoint 232.600

// Each color in a range between 0 and 255
msg.payload={red:255, green:200, blue:30};
return msg;