I believe Vermilion Red came into common use on the GN in 1958 at about the same time that the CB&Q adopted Chinese Red. With steam gone in 58 brightly colored freight cars had a chance of staying clean for a while.
The 1956 date for the use of Vermilion Red must be for the expermental schemes on the circus cars.
http://www.gngoat.org/circus_boxcars.htm
Glacier Green came along in the early 1960s
Big Sky Blue was adopted in 1967.
Vermilion Red, Glacier Green and Big Sky Blue as well as mineral red GN freight cars all lasted well into the BN era. In fact, Big Sky Blue GN wood chip hoppers were a frequent sight into the BNSF era.
Check out that number at the GN Empire.
http://greatnorthernempire.net....htm?GNEGNBooks1.htm
It looks like that car number was part of a series of leased 40 footers off of the E-L, likely from A.A Morrison. The cars leased to the NP and GN are often modeled with balck roofs and ends to represent the application of car cement (think asphalt roof coating) applied to keep these old cars water tight. Car cement was commonly applied when the cars were rehabbed prior to lease but not always to every car in a series. I doubt it is possible to know for sure which cars did or did not get car cement on their roofs and ends.
The atlas 8714 box car represents cars leased by the NP from A.A. Morrison at about the same time as the GN was leasing box cars. The Atlas model sports a black roof and ends to depict the application of car cement. Also notice the lease info in the upper left corner. Some of these cars were purchased at the expiration of the lease and the lease data was then painted over.
I have the NP cars. They are nice models. I am sure that the GN cars will be too.