Same color blue with three different names for a medium blue cloth and vinyl bench seat. Any variance you see in color is due to fading of the materials original color. Just look on line at the original color brochures GM printed up for all of their cars. One shade of blue in 1965-'67 for the interior as near as I can tell. Exterior paint was a different story as they had five different shades of blue.
Ecklers and Lutty's both show that there is a medium blue and bright blue interior. In the oldcar.com library it also shows 2 different blue color samples. Like you said, the interior is somewhat faded and the colors are similiar.