Help with restoring color to Eames Fiberglass shell - Gone Brown  

It is certainly possible, likely even, that the resin binding the fibers has turned brownish over time and prolonged UV exposure. That two different-colored chairs would age to the same "ochre" tone, though, does seem odd.
Posting some pics might help to better understand what you've described.
Sometimes heating old shock mounts thoroughly with an electric hair dryer can help to soften the adhesive and ease removal, though sanding is always the final step. Masking off the immediate area with blue painter's tape before sanding is recommended to help avoid scuffing surrounding surfaces.

I have just added 2 pictures white stuff is just the white adhesive residue. You have see the area the shocks were removed from is so different. The second pic is the colour that the chair is all over. I am stumped.

Yeah, looks like they've suffered prolonged UV exposure. Nothing can be done about that. Some of the colorants used faded more than others, too.
Any gloss left on the contact (upper) surfaces? When the fibers start to let go and the surface gets "scratchy", sanding and clear-coating is often the only practical solution to making them useable again. Also, it's possible that they're somewhat brittle and less flexible than when they were new. Inspect for signs of cracking in the usual spots.

Thank you, I would not say they are scratchy, still have an amount of shine. Are you saying then that nothing will bring the color back, not even sanding? Would you think the color change would be right through then?
They have no cracking etc, look in good shape apart from color difference.

I wouldn't touch them aside from adding new shocks. And, yes, the fading/darkening likely goes straight through. On the plus side, I bet they show great translucency!
Try to find a white or clear adhesive to mount the shocks. G-Flex from West System or another 2-part called "Plexus" might be worth a try. I haven't used either for this application, but both seem appropriate. Maybe ask shock mount supplier. I have used PC-11 (almost white) on shocks with steel backs and been disappointed. PC-7 is awesome, but it's dark gray.

Actually they are not that translucent. would you just do a light sand & recoat? was planning on changing to narrow mount dowel base, but this will leave the colored patches where the old shocks came off.
Is this discoloration common?

I wouldn't recommend sanding. I'd just leave the spots and consider them honest evidence of the chairs' history.
I suppose you could try sanding a small area on the underside to see if it exposes fresh color, but sanding will expose more fiber ends, too. And consider the labor involved in doing a whole chair never mind a set.

Thank you for you advice. It is a shame I will not end up with quite what I planned they were not even that cheap. But I am sure they will still look ok.

I know nothing about eames fiberglass chairs, but I live in a place with an enormous quantity of UV light. I think that you would have to sand very deeply to get rid of any evidence of UV damage. For instance light will pass through the glass fibers and deeper into the chair than if it were just resin.
I wonder if they were sanded a while back, coated in Penetrol, and now the Penetrol has discolored from subsequent UV...?

So if that was the case would I be looking at removing the penetrol. I have seen other white chairs that look similar over time with penetrol.
How would I go about removing that. I have also been reading about cleaning fiberglass boats that have discoloured with UV & they use a type of boat/car cleaner?

Just found these pics on modern conscience http://www.modernconscience.com/blog/tag/fiberglass-chair-repair/
Similar colour changing from the before to after.

Well, color me pink. I'd get on the horn to Modern Conscience and see if they'll divulge their technique if I were you. If all it takes is treatment with the right sequence of solvents and oxidizers, then by all means try it.
Experimenting on a small, unnoticed areas first is always recommended.
Please let the forum in on results, Good luck!

I have emailed them & hope for a reply. Will update here if I have success.