Bear in mind that a fingerboard may be stained and still actually be ebony.  Not all ebony is pure black, it often has streaks that are lighter coloured.  Some feel that affects whether that particular piece of ebony is suitable and some say it doesn't.  But many fingerboards that are actually ebony are still dyed/stained to have the currently popular pure black look.

Either way, though, there is only so much "AAA" grade ebony available because it takes a long time to grow and the forests are being depleted.  It has also become illegal to harvest or import/export in some places.  So, in the not too distant future, it is not impossible that ebony could become an unusual wood for fingerboards, rather than the usual.  Someday it may even fall under a ban, like ivory has. 

Ivory used to be used for some musical instrument parts, but now you can risk even losing instruments made before the ban if you try selling them or moving them across certain borders. 

It seems likely that in the not-too-distant future, woods other than ebony will become more common as fingerboards.  There are actually quite a few different woods that can be suitable, and some of them are more replenishable and have been less heavily harvested than ebony. 

So try not to get too attached to the idea of an ebony fingerboard being an automatic sign of quality, since it may not be with us forever.  It may go the way of ivory, tortoise shell and other materials that were once common in musical instruments.

Fingerboards also do wear over time, and can only be re-planed so many times before they need to be replaced.  Even though ebony is a very hard wood that wears slower, it will not last forever.

In any case, though, ebony does not turn metallic/silver (argent) when worn, nor will a lighter wood under black paint likely suddenly become metallic.  So the culprit is most probably the strings.  Hard to tell for sure from the pics, but it looks a bit like marks I sometimes have seen on my violin's fingerboard, and that wipe off with a little rubbing from a cloth.