I reckon there is an option missing, "how the vehicle has been used for the majority of its' existance" much as I like, for example, Matador gun tractors I have a soft spot for timber cranes. I don't see why everything has to go back to military colours Dave Weedons Rotti looks great in Sunters livery and I know of a Diamond T in a shed, that hasn't been out for some time, that looks good as a civvy wrecker, it would be a shame to paint it drab again.
People are forever wanting to know what the "correct" paint is for whatever vehicle they have got. It doesn't matter, paint your vehicle how you like, it isn't a "military vehicle" anymore.