Hi Keith, welcome to Outdoorking. I have the impression that reproducing ATCO green is a lost art, but if you read far enough down this English thread you will find what purports to be the answer:
http://www.tractorbox.co.uk/forum/forum_posts.asp?TID=6464

He asserts that Leaf Green, RAL 6010 is a perfect match. To see whether you agree with him, here is an RAL colour chart:
http://www.ralcolor.com/

The main problem is that Leaf Green is actually RAL 6002. RAL 6010 is Grass Green. I'm not all that sure either of them matches the ATCO I had long ago.

Last edited by grumpy; 01/02/13 05:47 AM.