Paint on their feet?
Seriously, I would assume that the green was a techie rendition of green and not paint. Paint would be unmanageable on so many levels.
The concept is awareness. I would assume that there is probably something like a small simple sign saying "Thanks for walking" or something to spread the idea. This was an expensive endeavor, and I bet they thought about a lot before it appeared.
Street art can be powerful as it usually evokes some sort of enjoyment. I hope that you can discipline yourself to take a more neutral view before judging. Personally, I would love to see less generic trees, and more icons of local popular trees.
