Ok, you lured me in from the thumbnail...had to take a look. :D I like the use of the chalks here, very creative. Great use of lighting to get the extremes on the left and base. Almost looks like clouds or fog rolling thru your photo. So, how'd you get them to stand up? I used some of these once and it was a pain to keep them in place. Used playdough on the bottom, which was fine until the playdough starting drying and hardening, then the little buggers would fall over. In your case you'd have some serious "dominos" going on! :D Good luck in the challenge.
I wish the green chalk was just a bit different tonally from the white. It is hard to distinguish them unless you really look - unless it is just my monitor.