Hey Jep,
Tim's correct, all Healey's had the same color chassis and body. IMHO,whoever told you about the green firewall and chassis is wrong. If your chassis is painted a color similar to the green engine color, then someone did that in the past. Did not come from Healey that way. This is all from the bible most of us use, "Austin Healey Restoration Guide" by Roger Moment and Gary Anderson. They also used Andres Clausager ( may have butchered that spelling) as one of their own references. I'd get the Heritage Certificate as that will tell you with no question what color your Healey left the works. Healey offered two greens for a 100-6, Florida and Pacific. Neither of those is metallic but guess it's possible someone got a special paint color and wanted a metallic green. But if they did, everything would be that color ! Good luck with the restoration and post pics as you go along !
Regards,
Mike
PS - you say your 56 is a 100-6 but did you mean a 100-4/BN2 as there was a Spruce green color available on BN1's and BN2's ? I have never seen it but maybe it looks similar to the engine green color and would make sense then that the chassis looks the same. Or maybe it got special ordered with the Spruce green paint since the first 100-6's were made in May 1956 and the original owner wanted the BN2 color no longer available on the new 100-6's ? Always something interesting with these cars !!!