On most of the 6 bangers I saw from this period, the majority were blue, except for the ones that people had painted orange. The way I always thought it was, is the 6 bangers were blue, and the v8's were orange, but we have a 78 with a 305 in the shop and it's blue. The breather would be black, the valve covers would be the same color as the block. I don't recall any other destinct parts that were different colors.
Robert