This is fascinating, if you have wondered what dogs actually see -- and maybe thought it didn't matter when doing agility or training your dog!
http://agilitymach.hubpages.com/hub/How-Does-a-Dogs-Color-Vision-Affect-Canine-Sport-How-do-Dogs-See
http://agilitymach.hubpages.com/hub/How-Does-a-Dogs-Color-Vision-Affect-Canine-Sport-How-do-Dogs-See