I'm organizing my zinc plating for my hk holden mainly the engine bay. Does anyone know what colour things like linkages for a powerglide is. They seem blue passivate but I've seen gold on some cars. Is there a difference if its a 186s gts. What colour should most components be?

As far as I know most of the bits are straight zinc, with a few in yellow passivate. Things like the heater cable support plate, heater motor housing, wiper motor housing, large washers on the crossmember mounting bolts are all natural zinc. The accelerator linkage is a bit odd, as the drivers side support bracket (on the Firewall) is natural zinc, but the bracket towards the centre of car and the accelerator control cross link are zinc yellow passivate, at least on the cars I've seen. I cannot help with the powerglide linkages, as I've never seen them.
Can you be a little more specific about which parts you are getting plated? If you are looking for historical accuracy, then you really need to identify each part, as there is quite a mixture.
Hope that helps.