Cub alone should also be accepted. We don't call the chicago sports team the "bear cubs"
Will Duolingo please make up it's mind as to what colors are called?
That's the difficulty of Korean colors. There is not a one to one correspondence, so they have got to make do with what English has to offer and adjust it to the most probable color you'd use for the noun that follows. Green for grass but blue for sky. Same word in Korean.
Not sure about the other sentence, but 곰 means bear and 새끼 is used for any animal offspring. baby + bear = (bear) cub.
Maybe the other sentence was talking about another baby animal?