Where did the phrase off color originate?
16th. cent. originally 'choler', early medical 'choleric' theory believing four 'cholers' and their balance (health) or imbalance (illness) was determinable by sight. 'Off choler' describing a generalized illness.
The term, "the color of the blanket" is not a sentence, it is a noun phrase. There is no possessive noun in the given noun phrase. The possessive form of the noun phrase is: "the blanket's color". Example sentences: The blanket's color is a bright blue. (the noun phrase is the subject of the sentence. These sheets will coordinate with the blanket's color. (the noun phrase is the object of the preposition 'with')