Regarding Fjord's, and all dun horses, it is important to remember that dun is a modification gene, and not a base gene. The modification gene has to act on a base that is already present, like black, bay, or chestnut. The different shades of dun are merely the dun gene acting on different base colours, not differences in the dun gene itself. What most people consider to be a 'typical dun' is bay dun, or dun acting on a bay base coat.

Red Dun = Chestnut + Dun

Grullo / Blue Dun = Black + Dun

Bay Dun (or just Dun) = Bay + Dun

Fjords do carry Crème as well, and you can get what most people call Dunskin and Dunalino.

Most Fjords are just regular bay duns, or brown duns, as they call them. They aren't, as a whole, lighter overall than other bay duns. There's as much variation in the colour of bay duns as there are in bays themselves. Fjords just seem to tend more towards being a lighter shade than a darker shade.

Regarding the manes, I do not know. Most Fjords haven't had a whole lot of genetic typing done on them, but I would suspect that it is a completely separate gene from dun, although it is possible that it is related to the gene that causes frosting in some duns.

As far as the primitive markings, those come from the dun gene (the dorsal or eel stripe, the leg bars, shoulder bars, etc.) The only reason that they are so prominent in Fjords is that Fjords are almost universally homozygous for the dun gene. If every horse carries the gene, then every horse will exhibit the markings.

Also, just as an aside, if you cross two Red Duns or a Red Dun and a Dunskin or Dunalino (what the Norwegians call Yellow and White Dun), you will never get a Perlino or Cremello foal. Perlino and Cremello require two copies of the crème gene, and Red Dun carries none of them. Two Dunskins or Dunalinos could produce a Perlino or Cremello, but Red Dun crossed with anything never will.