I know this question has probably been answered before but I am still in the dark a little. As I understand it the green label has no sear block and a large pin. The blue label has the sear block and a small pin. Are they both pre-ban? Are there any other differences? Also can an upper made for a green label be modified to fit a blue label (large pin vs. small pin), or vice-versa?
Thanks in advance for any help.

Besafe - I am afraid that it is not that simple. Welcome to the world of Colt. While it is generally true that Green Label rifles do not have a sear block and do have a large front pin, it is not written in stone. Colt did some odd things. The same holds true for Blue Label Colts. I have seen them with every combination of sear block, large front pin, small front pin and raised mag fence. My Blue Label has a large front pin. My friend has one with a serial number that is close to mine, but with a small front pin. The only way you will know for sure is to inspect the rifle in which you are interested or ask questions of the seller if buying mail order. With Colt there are no hard and fast rules.

except there the best!

Besafe,

A good source of Colt AR-15 Preban information is www.biggerhammer.net/ar15/.

Current Colt production (post ban) is still Blue Label.

Generally the "Green Label"guns are pre-1989.Sear blocks were installed in post 1989 guns until about 1997 (if memory serves).In "blue label"rifles that have the small front pin,the trigger group and hammer pins that hold the parts in place in the reciever,are a slightly larger diameter than earlier guns.This was to prevent people from converting these to M-16's.

colt, very strange...
i just bought a Colt LW sporter 223, 16 in barrel 1/7 twist

has large front pin AND raised fence around the mag release.

who knows what youre gonna get