Elvish blood is slightly more purple than human blood, but different enough to make a BIG difference in looks, given that Elves can see a much broader spectrum of colors than Humans can. A human could detect the difference in color when the blood was fresh, but not after it had dried.

I think the scene with the handprints on the altar is the one when Vieliessar does her vigil in the Shrine of the Star. What I'd been going for there was not that Elven blood was silver, but that the handprints made a magical impression on the stone (like the handprints in Neolithic caves, only with magic instead of paint).

I like questions. And since I don't want to jar people out of the story, questions are very helpful.