I don`t think you understood my point on being more specific about your search.We can dream up all kinds of colors we`ve never seen or seen once.Then,there`s shades of each color.I`m not trying to be ridiculous.I think its because you used the word "rarest",which narrows it down to a single color,that got me thinking the search has to have some bounds.If you asked,"What are some rare colrs",then we wouldn`t need to limit it.There are factory pack colors and custom mixes.You need a basis to rate on or what`s the point?You could say "Baby Blue" and there was a light blue in the first few years from the factory,but it wasn`t called baby blue by GM and there could be a thousand shades of just Baby Blue and some will call it Sky Blue.As I said,even the factory had a list of colors offered each year,some only one year,some every year,some only GMC or Chevy,and some on both but more years on one brand then the others.Obviously a one year/one brand standard color would be rarest.But,a special paint would be even more rare.A non-factory color could be one of a kind.
I can think of alot of factory 67-72 colors that i`ve seen alot less,if ever,than Grapefruit.Then,there was a Pale Yellow in the earlier end that isn`t called Grapefruit but is only a shade different.You see Grapefruit (late color) more than the earlier version.Clean67 has that color on his`67 CST/20 CustomCamper.Palamino Tan on GMCs was a carry-over from the earlier years.Like Paul said,that`s a rare one.The `67 GMC project I`m building started with a Palamino Tan clip from Nebraska that I bought.It had perfect Custom badges and I bet that truck would have been a rarer bird than most.The Special Paint color I mentioned,Light Grey,I`ve only seen on the truck I had.Add the factory Red whaeels and you`ve narrowed it down even more.But,if there were two ordered that way it would be less rare than a color I could go and have mixed today and put on a 67-72.Catch my drift?If you just want to know what is the rarest color of all possible colors,then there are alot of one-off colors and they would all be equally rare.So,the rarest color would be the one you never saw.
Here`s that Grey:
You might have seen another Light Grey truck,but without checking the SPID you won`t know if it`s a factory Light Grey or a repaint.
Here`s a Grapefruit Blazer I have:
This Green is a special paint used on a fleet of rental trucks.There were many painted this color,but it`s a rare color to see on anything but one of these.And,there are less and less surviving.A new repaint color could be mixed and shot today:
Here`s that Palamino Tan:
I`ve only seen this truck in this color: