Avalon Eidolon has marks on midrange speaker

Why not contact the company with that question? You could ask whether this would "color" the midrange, or whether the speakers would instead be expected to pass muster with flying "colors". :)

Eugene,
I hope it's not catchy! I don't think there's a vaccine available for my speakers.

I do not have those on mine (6 months old) but read here on AgoN that it is normal. Discolorations apperar over time and do not influence the sound quality.

I contacted Avalon Acoustics and that is what they told me

'Hi Eugene,
These marks are usually caused by ferril fluid being deposited on the back of the ceramic material, during use. As long as the drivers are still functioning normally there is nothing to worry about.
In fact the manufacturer of this driver has been talking about changing the color of the driver, as these kind of marks often lead people to think they are defective, where in most cases these marks are nothing more than a sign of use.
Lucien Pichette'

Thank you guys!