Color is only one aspect of a fluid's condition. On a rating scale, it is only about tenth in importance - however, the color change from "new" can help you in troubleshooting the system.
More important aspects of the oil such as oil viscosity change, contamination, water content, dirt content, acid number, additive package presence (change), oxidation of the oil, anti-foaming characteristics, etc are all more important than just color change.
Did the oil smell burnt?
If not, one possible scenario is some type of contaminant such as paint of a degrading o-ring might have changed the oil a black color. (I'm assuming that when you describe the color as black that it is an dark black like dirty diesel engine oil ladened with soot).
But since you have 'no leaks' the o-ring does not have much weight to it.
If you still have some of the 'black oil', put a drop or two on the back a some coarse poster paper (like business card stock) and see whether the oil still has dispersency remaining. The one or two drops of oil show form a quarter to half dollar oil spot in 2-10 hours and should not have any rings in it (rings like a growth ring in a tree trunk). If it does, then the oil needed to be changed due to contamination.
As far as is the pump going to fail before warranty?
I ran 140,000 miles on the original power steering fluid before changing (although mine was not black in color).
Good luck, only a phophet can answer your question about the life of your pump. I also doubt that a dealer would change it out just on the "chance' that it might fail.
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