My front step is made of black gray rock work and our flower pots leacked water that was a rusty clor and left stains on the rock that is white in areas and a rusty brown in areas. How can I get the dark color back?

Start with mild chemical cures like spilling some vinegar in a hidden area. If that does not hurt the stone but the stain remains try Whink or Raze in the hardware store area or grocery store area where they sell water softner salt.