That's interesting. The clutch hydraulics in my VW have a green tinge when I bleed them. They are using the same glycol-based fluid as the brakes (they share a common reservoir for the brake master and clutch master), and to my knowledge there aren't any copper components in that part of the system.
I'm guessing it's assembly lubricant. On my first bleed, the fluid was dark green. On the second bleed, it was much less green. The fluid was in there about the same amount of time, so it stands to reason that there's less of it now than before, leading me to believe it's a remnant from the assembly process.