Hi, Jamerelbe. I've always preferred plastic/acrylic/resin over any metal as the primary body of a fountain pen. My preference is based on look to the eye and feel in in hand. So, my own preference favors the Delrin or Acrylic versions (equally light) of the Decograph. The Decograph aluminum versions, though, are light (but not as light as the others), and one can't doubt their exterior durability compared with plastic/acrylic/resin. The battleworn Violet has an interesting look, but I'm not in love with the look, although purple is one of my favorite colors (especially when I was younger); I guess I prefer anodized aluminum over raw aluminum for eye appeal. I liked the performance of the pens, so I also wanted examples of each material in favored colors. I hope this explanation helps you.
Thanks @donnweinberg, that's a real help - now I have to decide whether to buy a Decograph before the current sale ends (a few models still sitting at $100 till midnight June 30!), or whether to hold off and hope for a future sale... I think you've convinced me to hold out for an acrylic version - though the red-with-black-furniture Al model looks pretty sweet!