One of the reference pages I found for car colours was http://www.cats-citroen.net/citroen_tractionavant/ta_colors.html
Looking at that, it looks like the factory only painted in Black (AC201 Noir) however it does appear possible that the car was delivered to the dealer in ‘primer’ and painted to the customers request
Looks like your going to have to carefully remove layers of paint until you get to the original top coat to be sure.