That is the coloring dye fading/wearing out. The technology to dye the concrete has changed so it lasts longer now.
No, that’s dirt and grunge getting ground into it.
http://farm5.static.flickr.com/4127/5062686419_2269dc30f3.jpg
Those used to be red brick, now they’re tire colored brick. And if those were solar panels it’s going to be hard for them to see the sun through all that crud.
