As far as the 1960 GMC colors go I did a lot of searching and reading before choosing the combo I have on my truck. The Olympic White with Canyon Blue was as far as I know a very seldom chosen color combo. From what I read it was considered "Too Pretty", if that makes any sense?
To support this line of reasoning, I think back to the "GMC Palomino" truck; which they only made for one year, I think?
https://www.google.com/search?q=1957...w=1440&bih=731
It was hard to use them as a work or farm truck. BUT honestly, because of lost or missing GMC records, we'll never really know for sure.
Below is a shot of my doors