I came across a conversation regarding the color "straw" in Cane Corsi and speaking of it as a rare color. Over the years I have seen the word "rare" and coat colors be used more than once, perfect example is Merle. Which isn't rare within the breeds it was supposed to be is now being touted as rare as a off color in breeds with no recorded history of this coat color.
other issue is when many hear the word rare or special they tend to want it, but purchasing a dog solely on popularity or coat color is nothing short of dangerous.
Imo, rare should never be used when describing a color. Chasing coat colors will only lead one down a path of ownership of a subpar dog.
I see all of the time the breeders say we have rare colors. It is done in a variety of breeds. This proves my point that not every that call themselves a breeder should be calling themselves breeders. These rare colors often mean that some other breed was introduced to the breeding stock. Examples are a white Rottweiler, white Presa, Merle pit bull. In some breeds the standards are being changed to accept the rare color or trait.