Avalon ,discoloration of ceramic tweeter

Do you live in a large city? smoke or cook near them? If not you may have over driven them causing slight voice coil damage that yes will cause a failure with time. Tweeter will also start sounding poor if damaged. So if sounds the same as before just run them. Unless a warranty is involved. You might have to contact Avalon ask there opinion.

I believe that Avalon uses Accuton's ceramic tweeter, so you could contact the manufacturer directly to inquire about this condition.

Light weight small diameter underhung voice coils are more easily overdriven. 1/2" is roughly the voice coil diameter (yep it is tiny - considering most tweeters VC are 1 inch).

As you halve the VC diameter then the surface area to radiate heat becomes FOUR times less. You tend to get thermal compression (distortion) and the tweeters blow all too easily. It is a bad design if you like to play music loud or fill a large space with music. Pro equipment nearly always uses larger diameter VC's and/or compression drivers (horns).

Possibly most of the ferrofluid is gone from your tweeter and it may be on it's last legs. Fortunately the tweeter does not do that much (midrange is far more important) it may be hard to hear any added distortion - try listening to piano carefully.

You burnt the living #$%&* out of them, Best to get the exact tweeters from the distributor and pop in two new ones. Just be careful to attach the wires correctly. I did the same thing but no color chage to my JM/Focals. The fix was very easy but not exactly cheap - and I am not a DIY guy, yet anyway.