Oxidation on surface of cable under clear jacket

No, I live in normal conditions.  This problem with greenery is not unique.  The manufacturer knows about it, so he changed the transparent insulation of the wires to opaque in new models.  The sound, as I know, is not reflected.  The problem is precisely in loose insulation and poor protection from the environment.  PVC insulation loses its tightness over time.

Your cables will still work, they simply will be brighter than what they used to be because the oxidation is a bad conductor and will shift the tonal response towards a litz wire configuration with is brighter than the equivalent configuration where there is electrical contact between the strand. Try them to see if you like the tonal response or maybe have them be recycled.

61falcon. I lived in northern VA. Summer humidity could get high, but home was air conditioned, so I doubt high humidity had anything to do with it.  

Felixa I will put them back into my system and give a listen.  AND I have a pair of Kimber Kable 12 TC (much newer) that I will compare them to, to see which I prefer.

I have 30+ year old cheap 10 and 12 awg speaker cables lying around, clear insulation, not a hint of oxidation, and I had some cheap 18 awg that was maybe 10 years old that looked like it was outside from day 1.

My understanding is the material and quality of the insulation determines how much oxygen gets in, which seems pretty obvious, but also good OFC should oxidize slower.

Quick Google says the oxide probably 10's of nanometers thick. I don't see that making a big difference to the conductivity. I would be more worried about the connectors. If they are soldered they will be fine. If they are a good quality crimp they should be okay too. Anything else could be trouble.

Seen it worse than this ....