Dating this arm shell swivel chair?  

Late 1950s
Shell color is Lemon Yellow or Ochre Light... difficult to tell from the lighting. Both colors are nice though. My suggestion would be to try to remove the tape residue (do not sand), and that's it.

Thanks for the response,...
Thanks for the response, woodywood. I'd say it's closer to Lemon Yellow than Ochre Light. It's not a bright yellow by any means. Is it safe to assume that beneath the gray paint on the back (I assume the factory did this to match the upholstery?) is the same yellow color?
Also, can you expound on your date estimate a little? What makes you say late 1950s? I personally was puzzled because the logo on the back of the shell is not like others I've seen online. It almost looks incomplete. See photo below.

I have a similar, once...
I have a similar, once upholstered, lemon yellow shell. Used acetone to remove paint from back. Required a bit of elbow grease, but came out beautifully.

Summit?
Upon unscrewing the swivel base, I found two small interlocking triangles on the base of the shell. Is this indicative of Summit production? There's no circle S mark, and also no Herman Miller lettering beneath the embossed HM logo.
Happy to have found another clue. 🙂
Back story on the chair: it was given to my mom for free (a friend found it at a garage sale, I believe) in the 90s, and we used it as an office chair. It then sat in her basement until maybe last year, when I asked to take it off her hands. I don't plan on selling it, and I hope I can restore it a bit, maybe put a rocker base on it (I'll keep the original swivel in storage), and use it in my living room or future nursery. It's certainly a conversational piece, and has nostalgic value for me. I'm also warming up to the yellow color, especially if I can get the paint off the back of the shell.
Thanks for your help, guys. 🙂 This a fun piece of history to have around, especially if it was made in Michigan, where I live.

I personally
like the swivel base, and find it one of the more appealing variables.

I like the swivel base as...
I like the swivel base as well, but for me it feels more office-y, and I would rather use this in a living room setting. We're short on comfortable seating! I really like that I have the option to switch out the bases depending on the need of the moment. The screws came off very well and aren't stripped, I was pretty happy about that, too. 🙂

to get the paint of...
It is right and important that you do NOT sand the shell. You will destroy and/or remove the GelCoat which will make the shell look dull. You also will losen microglassfibres which can harm your health pretty intense!
Acetone does work but might lead to crazes within the shell in Time to come.
I would recommend a thinning agent where you should do a little spot test first. If it works try to work with a compress that you can cover with foil so the thinner can t evaporate to fast and will do his job proper.
!!!!Always do this work with the right breathing mask and gloves!!! here is a link : http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSu7zK1fslxtUm8_x4x...
Try to tape the SHOCKMOUNTS first because the thinner might effect the glue or the mount itself. I will try to upload pic s from my chair later on.
It is a very nice model indeed. Sad that a restoration/conservation of the upholstery isn t possible since back then they sawed up the cover first and filled in the foam later. It is hard to do it even for trained upholsterer without the hardware there used back then.
Good luck with the paint and enjoy your chair for years to come.

Wow--
So, my daughter just bought an old HM shell chair on a swivel base with casters and we are trying to figure out what's original on it. I have never paid much attention to these but I knew there has been a lot of discussion about them here.
Anyway, hers is nearly identical to the OP's chair, down to the lemon color on the inside and the dark gray paint on the outside. Same gasket around the edge, same wire thing holding the upholstery onto the chair, exact same base style and materials.
The upholstery is a really nice nylon (?) hopsack in charcoal gray. It has a heavy muslin backing with latex foam (all dried out) between.
The fabric is in very good shape, just a little fading around the top back edge. I think she should keep it but she would like to get the foam replaced. I think that has to be done with molds so that it will keep its shape and not boing back out of the chair when you get up! So I dunno...may have to just live with it.
I have not looked closely yet for a molded mark but i did seem what looked like gummy residue from a paper label. Maybe.