you need something more aggressive than a green scrubbie. HD or Lowes sell emory cloth packs with a coarse, med, & fine grade for a few dollars. I typically use a 120 grit type that comes on a roll. Also clean the buttons with a tooth brush/mild degreaser. Simple green is abit caustic...
Those discolored areas would scare me. They possibly point to a metallurgy issue. If these brakes get used hard, I would consider new ones.
When looking at the disc it looks more like something going on between the holes in the disc and pads. It looks like there's a reoccurring pattern due to some holes.
