Not bad at all, well done!
Can't help with your thoughts though as I've not been down that road, though an overspray of any clear form of varnish should darken it a little. If you do add a tint of green, mix it up in a small jar first to ensure even distribution and you will only need a touch of the green, and then try it on the Hampden first, letting this dry first so that you can see the effect. If your happy, then go for it with the mix already made up.