Nice Fossil Hajar, I wish we had those here. Funny how nautiloids like these are not referrred to as heteromorphs. Aphetoceras with open coils and a ventral siphuncle, and Plectolites with a dorsal siphuncle, are examples of Tarphycerids also.
Yes, in this case each of those red bands occurs at the edge of a septum. I don't think the red bands are actually at the surface of the shell (with its fine growth lines), but are visible through the calcite. Have you ever come across something like this?