Are some older Eames shells suppose to have a painted back?  

Some of the upholstered shells had painted back and had metal rings and tape to keep the upholstery on the shell. Fortunately, these were not drilled. I had one in lemon yellow and removed the paint. Here is the old thread that talks about this.
http://www.designaddict.com/forum/General-discussion/WEIRD-Eames-shell-b...

Thanks. Hmmm.. seems weird as I don't think this one was ever upolstered. But some of those others have the same paint job.

if the shock mounts are painted then its prob been spray painted.
beautiful color

That's what I thought too about the shock mounts, but I've seen this on others consistently . Hmm

The chairs with painted backs had upholstery, but not the glued-on kind. It was a removable slipcover kind of arrangement, with a wire tying it down underneath. The paint is often gray.
More about them here: https://modernarmada.wordpress.com/2013/02/10/eames-fiberglass-shell-cha...

Is this a random tinyarmada reference, or is tinyarmada now toomanychairs?

Random. I'm just me.
I do have an armada of chairs, though. Does that count?

Too bad. I miss tinyarmada's posts. I believe it was a tag-team account.

That's great! Thanks for the link. Very cool.

If you have access to the 1955/56 Herman Miller catalog (either original copy or the 1998 reprint), the section on the upholstered fiberglass armchair has a notation saying that all versions with dark color upholstery in fabric or vinyl will have a black painted applied paint finish at the back while the others with light color upholstery will have an applied beige paint finish.
The examples you have are definitely not consistent with a factory applied paint finish.

Minimoma,
That's funny, I was just thinking that Joshua's examples were VERY typical of the several upholstered shells that I have seen over 25 years or so. Right down to the painted shock mounts! (I have this same catalog, but it didn't make me feel like Joshua's were any different) Up close, the lighter ones look like a "fleck stone" or fake granite type of surface.
It might be possible that from year to year the treatments to the back changed a bit?
Also, it is worth noting that there are many early arm shells (upholstered in the same manner) that were not painted on the back at all.

Very interesting!