I am sure you will find that the boom has been re-painted over in yellow mainly because of that completely yellow painted bottom rivet Kiwi. On these Cranes the original boom color is always still seen in the recessed center of that base crane mast rivet, but the outer lip factory riveting to secure the boom to the Truck body removes most all of the boom's visible outer rivet paint when they are factory spun.
I think this Crane is a nice looking "custom" that was done by someone post factory, but the completely overpainted boom's rivet center screams purposeful deceit by a collector looking to create an oddity to fool others. I like the model's colors, so it can be displayed proudly for what it is, an interesting custom one off.
Please check the silver body as well for over-painting with a different shade of silver that was done many years ago, not recently. The front base rivet has no deep center hole to it, it's too flat finished rivet seems more Superfast style than those found during the period these cranes were done from 1962-65. There is something not quite right about this front rivet's center without standard Lesney tooling having been used to spin it.......
Orange will dull with sunfade and become lighter in shade, but fade to a brighter YELLOW as this one seems to have been pictured here????

kwakers