... should those scuff marks be yellow?
... the scuff marks had to be silver because of the silver underlaying AII (UV protection)?
IMHO,
scuff marks were fabric (canvas/beige) colour and yellow. I-16 fuselage and wing fairing wooden surface were protected from moisture by a layer of fabric. Fabric was glued to wood with yellow nitro putty, then it was doped with several layers of clear nitro varnish (AI-N), leveled with more yellow puty and finally painted with 2 layers of pigmented AII nitro varnish ("AII Protective Green", "AII Light gray" or "AII Light Blue"). So, if green paint was rubbed off, there would be a layer of (quite strong!) fabric first, and then under the fabric there would be a layer of yellow putty.
Silver "AII Al" as UV protection was proposed by VIAM in 1940. Orlov mentions 1940 as the year when it was introduced, but this is not confirmed by museum exhibits (Vesivehmaa MiG-3 made in 1941 before the GPW, or Bourget I-153 wing made in 1940). So,
silver UV protection layer is almost certainly impossible on 1937-38 I-16s...
HTH,
KL