under the vinyl roof

the buildsheet & the gm documents show that my 72 gs came from the factory with a vinyl roof. the fellow i purchased the car from replaced the "original" vinyl roof with a black one. a week ago, i peeled the black vinyl roof from the car as it is being repainted over the winter. i used 3m adhesive remover to dispense with the glue. two cans later and the glue & cotton are all history.
guess what i found under the vinyl? yellow paint over primer? huh?
the car was originally flame orange, then silver, and finally fire red.
with any of those colours, why would anyone paint the roof yellow.
the yellow appeared to be two different colours - bright yellow over pale yellow over gray primer. we determined that as we sanded the roof down to bare metal.
any ideas as to why? a friend suggested that the yellow was glue for the original roof.

 

Yellow paint may have been a bit of extra insurance for the owner who restored the car before you. Who knows?
We primed mine & painted all around the edges & up to the factory seam for the quarter/roof joint. Probably just as easy to paint the entire roof.
Cowl tag will show exactly whaich colours the car was new.

 

Is it possible that a chemical reaction ocurred? I have heard of others painting the surface (where the vinyl top will eventually go) for corrosion protection and using a leftover paint to do it. But then again, why wouldn't someone just spray the color on the roof surface that was already planned for the body (meaning no further taping or masking required). If you sand elsewhere on the body (jambs, etc.), do you come up with a yellow color?

 

Whoever did the last top replacement probably had some yellow left over from another project. Cheaper than buying a quart being it would be covered by the top.

 

there is yellow paint on the a-pillars also. u guys probably have it correct. the previous owner spayed the roof & a-pillars with yellow paint left over from a previous project. there is red paint sprayed almost to the roof/quarter seam. however, brown primer covers the seam - he had replaced the original with full rear nos quarters, back in the early 90's.