I have a couple of wheels built up with spokes as Ken describes. My first impression was that they were galvanized spokes that had corroded but then I took a Scotchbrite pad to one of the spokes and incredibly it cleaned up to an acceptable level, with some tarnished spots but decent enough that I probably won't rebuild the wheel with new spokes. My current thinking is that they may have been of a lesser grade (in terms of stain resistance) of stainless as Chuck mentions.
When I was on the market for stainless-steel kitchen accessories for a commercial project, a sales representative explained that the higher the carbon content, the stronger but less rust-resistant stainless steel becomes. He also said something about the content of nickel in the mix, where nickel will make the stainless steel more stainless but more expensive.
Carlos Ovalle
Long Beach, California, USA