That tree is bigger than the castles down below. So it is a bit of an yggdrasil world tree. I feel the top is a bit barren. Is it rocky up there? where is the source of the waterfall?

Color... hmmm. I feel that if the cliff is brown and the city below is grey then a lush green up above might be interesting. It might balance the image out. Although it might also dominate and make the more important city less dominant. Worth a try?