Excellent choice! I was sure you would find a solution. It is indeed the colour that suits best: it doesn't catch the eye, leaves all the presence to the map, without being invisible... Well done!
As for the gems, I don't know what you have in mind, I think they're not bad at all. Perhaps a little light enhancement, white (almost 100% opacity), in small touches where the reflections are the strongest could do the trick?
I also hope that you will find the time, because I think the map is really superb and it corresponds, in a better way, to what I had in mind at the beginning! Nice work!