(source)This information from the handler is coming at the dog fast and furious. Except for occasional verbal information, all of the information given is non-verbal. The dog needs to respond to this information immediately. Fast dogs cannot take a second glance to see if they read that information properly. To help the dog, the handler must not visually blend into the background, but must stand out clearly and sharply to the fast running dog.
I learned this interesting concept from my fast dog, Asher. We usually compete in horse arenas on brown dirt with dirty white walls and fencing. I noticed from videos of our runs that when I wore one of my favorite agility shirts - a tan shirt - Asher would seem to not see some of my physical cues. He wasn't intentionally ignoring them. He appeared to simply not see them. Yet, when I wore tee shirts that contrasted with the background, he appeared to see all of my physical cues. After several weekend agility trials taped with my tan shirt and other contrasting shirts, I saw the pattern and discovered that Asher did better if he could see me better.
Of course, this is obvious when you stop and think about it.
Once discovering this pattern, I remembered reading that dogs don't see the color spectrum as humans do. I decided I needed to know exactly what colors dogs did see.
Dogs cannot see reds and greens. Instead, reds and greens are actually shades of yellow or brown. Knowing this, I am able to choose my agility trialing wardrobe with the idea of helping my dog more clearly see my non-verbal cues.
The implications for dog sports are obvious, but can also be useful for house dogs too! I recommend checking out the full article if you have the time.