The green numbers might have come in 1981 when the shift adjustment knob bracket was changed to not interfere with the New F-1 camera. If so, then there might not be any optical difference. Quote from the last link below:
"The early version of the lens will not rotate without the shift
adjustment knob hitting the AE finder Unless you put something like a
M5 or M10 extension tube between the lens and the body. Which of
course would effect your focusing range. The later version with green
Feet numbers has a slightly different braket to move the knob forward
on the lens ending this interfearance."
http://tech.groups.yahoo.com/group/CanonFD/message/45681
http://tech.groups.yahoo.com/group/CanonFD/message/45709
http://tech.groups.yahoo.com/group/CanonFD/message/45739

Not worth the price difference IMO, unless you think the knob will get in the way on your camera.

lenticular11 wrote:
I bought one from Eastern Europe on eBay at a relatively good price. It was and is in mint condition. The EdMika brass adapter is not cheap but makes conversion very straightforward for those of us with less mechanical skills (he supplies a 2nd ball bearing for good reason - don't ask me how I know).
CameraServiceOne.com in the UK also convert this lens to EOS

I love the lens and haven't used it enough but will do so more in the future (too many lenses, too little time).

I used this site to help convince me of the IQ of this lens - http://forum.mflenses.com/infinity-test-and-others---canon-fd-35-ts-f28-t44513.html



That is my lens.
Highly recommended CameraServiceOne.com.

Found one at a reasonably reasonable price , (£440), and supposedly excellent condition, later version, on it's way to me now. Just the expensive EdMika adapter now!