Copper can be very reactive in the right chemical environment, such as
our plumbing system over about 20 years. After clothes & hair &
ceramic sinks going green She got fed up and all copper was removed
except basin taps (which etch away every two years). Now no more
green. My guess is the stain is a normally soluble copper compound and
the clothes & hair were coloured from copper stearate (soap). That
BTW is water from our well which is like cool, clear champagne to
drink, but is hell on copper.
Phil