Yáʼátʼééh! @ConorHoughton, I agree with your translation. And, as @Judorange123 said, the Navajo for "black bear" has a nominalizer for the verb łizhin, then it becomes łizhinígíí.
Then, the Navajo does not use an adjective here, but I think this is a verbal phrase or a combination of a noun and a nominalized verb (or nominalized adjetival verb, because łi is adjetival and ígíí is a nominalizer), but not a sentence, so "the bear (the particular one) that is black" (shash łizhinígíí), instead of the sentence "The bear is black" (Shash łizhin):
Shash łizhinígíí (Ursus americanus / American black bear)
It seems that the Navajo for "polar bear" uses the same structure.
1. polar bear
"The bear is black" is marked wrong, but presumably this is also a good translation?