Thanks for the reply PeteB... Wanted to respond to your reply and questions posed... so the best way is just to paste your full reply and insert my comments... here goes... :-)
I am in agreement with Silk City that some foam over early in the run is a possible cause. So am I also in agreement... especially so since the re-distillation removed the color.
I have never used vinegar to clean but it would not surprise me at all if the vinegar reacted with the copper to give the greenish tinge... Vinegar is what I have always used, cheap, effective and safe, especially if it was some time since the cleaning.
Was this the very first run with a new still? No... ran a cleaning run with vinegar when still was new... no color was imparted... and ran 96 gal of apple must just for stripping runs followed by double distillation (2x spirit) mid-April to early May... the still sat unused until end of June when I started the next stripping... but performed another cleaning run with vinegar and a rinse run with R.O. H2O prior to the first (and only) stripping run that color was observed.
Could be weathering products on the copper, or weld byproducts, that apple spirit was better at stripping off than vinegar was. Not likely given the manner of cleaning prior was the exactly the same as previous batch.... we're back to the likelihood of a still puke
If not new what was the previous run? Apple spirit may have been better at stripping leftovers off than vinegar was. Previous run was Apple.
If there is any moisture left in my still it often drips blue or green from the condenser the next day, and I can be sure that the start of the next stripping run will be a greenish brown colour. It is just at the start of the wash run so it really doesn't matter as the spirit run will fix it. I've observed that as well between consecutive runs when the still was left empty but wet overnight... this time the still had sat unused for ~1.5 months... it was bone dry before I performed the cleaning and rinse.
It would be interesting to understand the chemistry of what was happening but in the end if the spirit tastes and smells great then it is unlikely to be of concern. I agree! :-)