There is no way you can allow testimony based on speculation like that to establish the *source* for a fiber.
Even if the witness told the prosecution of such a blanket, defense would be able to suppress it from the jury because it would be pure speculation.
For your scenario the item would be alleged to have been in DW's house or possession at one point and now is no longer there. What kind of evidence is that? For all we know, they did tell police and/or prosecution of such item(s). No way would a judge allow them to testify to a jury about it, though.
But wasn't Feldman speculating that the orange fibers may have been from the shirts worn by the people in the pictures?
That is exactly what the PROSECUTION is attempting to do. They have no facts, no proof, it is all speculation.
Tell me if I am incorrect.