Chris, sorry I can't answer your question with any surity, but I believe it would have been the Austin green color on the MKI. I don't have a copy of "Original Sprite and Midget" by Terry Horler which is the accepted authority on original parts and colors. "Available from Moss http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=38238 "
I've noticed that this board doesn't seem to get as much traffic as some of the other MG boards on the net. For questions on authenticity especially for the early cars I find the guys on the MG Enthusiasts board very helpful and knowledgeable. http://www.mgcars.org.uk/
You can access the bulletin board without joining, but it's free and no real personal information is required to join and you then get access to the archive files.
'73 Midget (V6)
'59 MGA (I6) under construction
"There is a fine line between a hobby and mental illness"