Is this Colombo Tube Chair original?  

The Original
appears not to have screws on the inner rims, unless they've been added later ?

It looks original.
Or...it looks like the one at the Metropolitan Museum.
I was rather impressed with it.
I had never seen one in person...
I'll look for the photo.

Robert,
In your pic you can see that the rims stop the metal braces from slipping off, unlike the rims on the chair in question. Maybe the rims were replaced completely sometime. I never heard that there were knock offs of this one.
I agree with you rockland, it's an impressive design, just needs some space.

Yes, possibly replaced
the rim looks continuous on the original yet in two pieces with each of the 4 ends held by a screw on the yellow one ?
The rim looks to be moulded with the tube, so I'm unsure as to how they've replaced it- or why they would use screws in PVC?

yes, here's a good close-up...
yes, here's a good close-up of an old one:
http://blog.ounodesign.com/2009/04/24/joe-colombo/

I just sent a mail to the...
I just sent a mail to the seller and asked about the materials and the age of the chair.
Let's see
EDIT: I just realised that the wooden knobs seem too small; maybe this was someone's DIY-project?

The foam edges
and upholstery do seem sharper on the originals, despite their age.

and who the hell says good...
and who the hell says good design has to be comfortable?

is the armchair located in berlin ?
is the armchair located in berlin ?

I wonder
whether it would configure as a chair as opposed to just a chaise..

should work as a chair,
as pictured below.
Also: Despite I've never sat in one I'm bold enough to claim that it might be comfortable after all.

Oh, I know
how it works, but am wary of the fact the yellow one has all its components flat on the floor, and is not pictured with any of them raised in the chair configuration- do the assembly parts do their job ?

Right, good question! Too...
Right, good question! Probably too many question-marks to actually buy it...

I Really
do think it's a home made copy- maybe ask what the inner tubes and rims are made of?
If they're wood, as I suspect, you have your answer