One of the most common grammatical errors I see in the writing of students of all levels is the lack of agreement of adjectives and verbs when "each" is the subject of the sentence.
"Each of the cats are calico."
This sentence is incorrect because the subject is "each," not "the cats."
Therefore, the correct form of the sentence is:
"Each of the cats is calico."
If you get confused, remove the words that modify "each" and read the sentence. In this case, the sentence would read:
"Each is calico."