Yep, as evidenced by the color of a corroded penny!
C’mon Bill. You have secretly been harvesting all the envy from those that visit your garage 
Well, I don’t have that garage any more so maybe not so much. Sure miss it though! I am going to check some other vehicles when I get the time. Any one else waking up a sleeping cat might want to see what is lurking in your tank…
Metals like Cobalt, Copper. Nickel and Manganese will change color in a solution if their degree of oxydation changes… and yes Copper and Nickel can turn green, Copper would be a bluer geen than Nickel that would bear a yellower undertone… Well at least this is what I recall from my first class in mineral chemistry… back in the days! And I think Manganese was forming pinky-red solutions, but this is so far that I could be mistaking and I have no clue if there would be any Manganese in Stabil… Nevertheless we all can see an effect of this when copper roofing change colour from brown (newly installed) to green after aging (oxydizing) during a few years.
I’d say transmission fluid with dye added for leak detection