Have you tried asking them why they went back on the agreement to pay half and explained that you had to foot the bill for all of it? I dont think you would be able to go onto their land to paint the other side, but i cant see why you cant say.....remove a panel, paint it and put the yukky colour their side. No doubt they will then paint over it but at least you would have made your point. They are being tight and unreasonable. A friend of mine had trouble with a neighbour like that and rigged up a security spotlight shining right into their bedroom and hung things infront of the sensor so it was going on and off all night! Dont you think that was a really naughty thing to do ? !!!!!! : )