JSON - how to, variable value (again…?)

This is probably very simple but as a novice I just can’t figure it out.
I have this home automation device that can control the settings of Philips HUE. I’m trying to send three values (hue, brightness, saturation) as variables but no success.
Sending (using “PUT”) fixed values like in the attached example works fine.
But how do I use my three variables, that my device has named in1, in2, in3? (red, green and blue squares)
I want to be able to let my system generate these three values and then send it to my lights when I choose to trigger it.