Black foamy power steering fluid means what
The presence of black foamy power steering fluid indicates that oxidation has occurred. It is also a sign of the presence of water and air in the power steering line. You can find more information on power steering fluids at http://www.doityourself.com/stry/5-symptoms-of-power-steering-failure#b.
It could also be that you put the wrong type if fluid in it. A common mistake.