Is Marshmallow Sofa with coloured discs more...  

As I understand
Multi-colored vinyl is the standard issue. So any leather option would presumably cost more.

Actually, multicolored is only...
Actually, multicolored is only one of about 30 available colors of vinyl. Each of those colors -- along with a couple dozen colors in two other fabrics -- costs the same and is equally "standard".
As woodywood said, though, leather is a more-expensive option that adds $1000-$2000, depending on the type, to the base MSRP.

Okay, well
The multi-colored version is the most FUN!!

Has anyone ever
found an original vintage one? Herman Miller made very few of 'em during the time they were in production.

I had a vintage white one...
I had a vintage white one for a while. I sold it through an auction house, though.

strange diggs
I know of two that ended up in restrooms... no doubt the only environment in which they might be considered the most comfortable seating in the room. They make wonderful sculpture, but an awful place to sit for more than 5 minutes.

Peacock Chair by Verner Panton
Is manufacturer Plus-Linje now defunct?
Or maybe it is no longer made with multicoloured pads?
http://www.verner-panton.com/furniture/auctions/4104304/

Totally different look
I personally don't care for the multicolored version. I think it looks too "zany" whereas the solid color version looks like what it is, an exploration in seating solutions. I also have to disagree with poach. While not the most comfortable seat ever, it's hardly unpleasant. Even after an extended sit.