I don't think anything will bleach concrete. Contact your city again. Or you can paint concrete.

I just cleaned my concrete in front of my garage, I couldn't stand how dirty it looked but I refuse to use toxic cleaners like bleach outside the home, a friend recomended a eco-safe product called mold & mildew wash by wash safe industries, I soaked it down, let it sit for a while then scrubbed it with a deck brush and hosed it off. It's white as can be, maybe it will work for you.

Here is a link that might be useful: www.wash-safe.com

Under my deck is a concrete patio that would get awful, yukky, stained from wet leaves that sat over the winter.
Clorine bleach fixed it in an hour or less.
And remember that "toxic" clorine bleach is the same thing that's in your swimming pool, some dishwashing detergents and used to purify some municipal drinking water.
Just pour on the bleach, let it dry and rinse.
BUT if the stain is paint or oil or tar, it won't touch it.
Linda C

It's not a stain per se. The concrete in this area was never uniformly whitish/gray. It cured with dark blotches over about half of it. So I don't think it needs to be cleaned, it really needs to have the concrete bleached out or maybe recoated with concrete? Would that work?

We have a concrete sill that is dingy looking and some stain marks on our lannonstone that surrounds our front door - my husband cleaned them both with CLR and they look good as new. He had to do a little scrubbing with a wire brush, but with a little patience it looked good as new. Hopefully the colors you are referring to aren't permanent.

Good luck.