Cafejim
Just found this thread. I also have the same discolouration on my chain. I don't think mine is from overheating, it looks more like the chain had a copper coloured coating on it from the factory which is just worn - I could be wrong though but you are talking significant heat to generate a colour change. You would probably smell burning chain lube before hand - if there was any there. :hammer:
However, this site may be worth checking out if you are worried:
http://www.sprocketcenter.com/c/1240...sst-99-07.html
I bought an 18t sprocket from them and they were very helpful. I am seriously considering a new chain because mine has spat out two 'o' rings. I am leaning towards the RK simply because it is looks to be better value than a DID. I would love the bling

but would have trouble justifying it.
That said, I would seriously doubt you need a new chain with such low milage. Check you "o" rings carefully after cleaning you chain, if they look in good condition its highly unlikely that you have an overheated chain.