Can any one tellme what is the correct color of the underbody for my Jan 66 built 66 SS .... semi gloss black or body color ?? appears to me my car may have been some shade of black but car has been repainted with some type of black rust proof paint 10 years ago so hard to tell

If your car was built in Oshawa then it should have body colour underneath, in the trunk, and on the firewall. Because of our climate GM Canada did it this way, and often in enamel instead of laquer (enamel paint is denoted by a 9 on the cowl tag beside paint if I'm not mistaken).
For U.S. cars I'm not sure but have been led to believe that they were primed underneath and had body color overspray that faded towards the driveshaft tunnel.

Thats great info ..... I was hoping it correct to paint it body color ...yes my car is Oshawa built...the firewall is still body color are you saying trunk never had spatter paint in it ?? no question side walls of trunk are body color but trunk floor has been painted with some kind of damm tough black rust prevent paint ....... I owned this car 30 years ago and just got it back ( been sitting in a farm building since 78) and I can't recall the trunk being spatter painted but not sure of that ....... My paint code is " M" Aztec Bronze which I believe is DuPont 4707 LM I always thought it was lacquer and the way the paint is brittle& cracked after all these years I am sure it is Lacquer.... do you know if M is for lacquer??

Again Thanks

Aztec Bronze, http://www.chevelles.com/forum/cool.gif
I don't know precicely, but I suspect that the extra colours offered in Canada were enamel. In the U.S. there were 15 colours but in Canada there were 18. Incidently my '67 is in Verde Green, a Canada only (maybe a Buick colour). It has a '9' adjacent to the 'JJ' paint code on the firewall, which means enamel. Perhaps only in the States did they say 'Magic Mirror Laquer'.
As for the black in your trunk it sounds post-assembly. Through '67 they didn't use spatter in the A-body trunks in Canada, eh?