Dark areas

On most light colored carpet ive notice dark areas that occur in areas where the  there might be a kid sitting playing in the same spot, or light traffic areas.  It isnt grease or oil, and I cant for the life of me seem to get the color as light as the rest of the carpet.  Ive tried a few different traffic lane cleaners with no luck.  its wierd.  It is even on my own carpet.  My wife thinks it is the dyes from the Black socks I wear.  Anyone else know what this could be? 

I bet its just worn out, wear spots will look like dark areas on lighter carpets for sure. Usually is a trail down the hall leading to the bathroom or bedroom, in front of the kitchen, infront of the couch and a circle where a computer chair would sit.

All you can do is grab a grandi groomer and try to bring the pile up as much as possible too look good as you leave.