is it true that if a dog has a black or partly black tongue that it means it’s part chowchow?
No. I’ve seen partially black tongues on other breeds - notably small terriers, like JRTs.
Here is an article on the subject:
http://www.columbusdogconnection.com/BlackTongueDebate.htm
In short, there are a number of breeds that have at least black spots on the tongue.
Nope, doesn’t mean anything. It’s just extra pigmentation in the tongue. My old lab had black spots on her tongue, it’s fairly common in some breeds of dogs.
Yep, my most definitely-not chow poodle mix has black spots on his tongue 
No, I’m pretty sure it’s possible in a lot of breeds, genetics mostly. I know a golden who has just enough extra pigmentation to make his tongue look purple! (it’s not lack of circulation or anything, the owners had it checked out)
This is a myth that started because it is VERY common for a chow to have a black tongue. The popular Lab can have black spots as can German Shepherds and a variety of other breeds. My dog has black spots on the underside of her tounge and is a boxer mix (most likely lab).
