Gold Banded Black Pens

It is just like a standard: classical fountain pens, with black body, and gold band or trim. There must be historical thing about that. Or just for commercial reason?

Here are my black pens collection, listed from left to right:

1. Montblanc Meisterstück hommage à W.A. Mozart
2. S.T. Dupont D-Initial
3. Platinum with maki-e depicting an asian phoenix [Link]
4. Montblanc Meisterstück Gold-Coated LeGrand 146 — a standard for fountain pen enthusiasts [Link]
5. Platinum #3776 Century with music nib
6. Sailor Profit Junior depicing a cat on its nib [Link]
7. Omas 1930 [Link]
8. Conklin Duragraph / Duraflex with black nib