Working concept for reference only
I doubt I will do much more with it as Amazon have recently announced native colour control. Though it is only available in the US so I (living in the UK) will not be expecting it any time soon :(
It does work but requires an open port to your local network in order to communicate with the Hue Bridge (ideally via a proxy) because Hue don't seem to let anyone use thier remote api ;)
It also needs you to hard code the groups and lights into the script. Which was fine for my general use, but it is a bit clunky.
But if you want to learn more about making a Skill allowing you to say "Alexa, ask colour controller to change living room colour to dark bluish gray" then this will help.