It's actually very fascinating to read about how different a dog's vision is compared to our own. I apologise for continuing the necro-post and bringing up a post which is over two years old, but for anyone who hasn't seen this post I thought this would be worth a read.

In regards to what Lurcher talks about with dogs defecating, there was a report published in 2013 which really looked into this. It found that both male and female dogs defecated in accordance to magnetic fields, and is the first real study to prove some affect on magnetic fields on mammals. The link is attached if anyone would find this interesting. It would certianly be interesting to find out if dogs can see the fields or have some form of inate ability to sense them.

And to touch on perrirjinnie's comment about colour, there were studies done which found that dog can see some colour. Due to the number of cones in their retina, they can see primarily in shades of yellow and blue. It is because where we have three different types of cones, dogs only have two. So the spectum of light waves that a dog can see is a lot smaller than those which we can detect. It's quite interesting to really look into it. I wrote a post on my blog looking into it which is why I'm so interested, but linking to that would seem very self promoting so I'll link to another post for anyone who is interested.