Cadillac built those for funeral homes, as a "flower car" to haul the flowers to the grave site.
Of course they were black originally. Since it is all GM, it was not a big deal to make them with some El Camino parts. Built on the same line as the limos and the hearse, just a few changes to make a vehicle that could haul large flower arrangements.
Since the family and general public never rode in them, from what I heard they are not great vehicles, and rather spartan.
I get compliments on my El Camino at least twice per week. The 67 pulled in next to me at the convenience store. His dad bought it new. It now has a 454 up front not the original 427.
I recently did my 390,000 mile oil change.
Almost broken in!