Appropriate color for Swedish swivel armchair?  

Any color you want would be ...
Any color you want would be fine, just avoid patterns that aren't appropriate, like florals, plaids, stripes.
Wait, no, not any color would be fine, now that I think about it. Pastels are obviously out. Black wouldn't look too great, plus it shows every speck of lint ever made. I guess I would just go for something muted and earthy, or a rich hue like royal blue, red, deep yellow---whatever goes well with your other stuff.
But mostly I would look for a high quality fabric with as much wool content as possible. I hate cheap fabric.

I vote for orange
I vote for orange

Beige or off-white is always right.
A cool color (cool as in opposite-of-warm: a muted turquoise or teal) would be nice with your wood floors, but of course the color choice should ultimately coordinate with the rest of the room. Shades of blue look great around wood, blue also has the advantage of being a flattering color to whomever sits in the chair, and the right shade of blue would also be "period".
But, I still vote for oyster.

white
.

Mark
That fabric is Knoll's "Arno", all wool and very, very nice stuff. Doesn't wear terribly well though, and it's kind of scratchy--but worth it. I just upholstered a couple of chairs in it.
Taupe or gray tweed is the best for hiding dirt and lint and still goes with just about everything. Some would call it boring but I call it classic. And you can put a really bright, interesting throw pillow on it and change that out as often as you want and not get sick of it.
I actually like the mustard yellow of the original.

Spot on, spanky!
You are correct, the textile is Knoll Arno. It's divine to the eye.

wool
ever lead to problems with moths?

moths
I think moths generally don't attack if the item is in use. Like, you don't see moths on a sweater you're wearing regularly, but if you put it away for the summer they will have at it.
I've reupholstered a lot of old furniture that had wool fabric on it and have yet to notice any moth damage. Maybe upholstery fabric is mothproofed...? I dunno, I never thought about it much! Too busy dealing with moth-eaten sweaters.

I am, too! That's why I now...
I am, too! That's why I now look at wool with jaded eyes. But if furniture doesn't seem to be an issue, I just may go for it. Thanks for the feedback!