When a person is wearing two or more articles of clothing which are blue. Like when someone wears blue jeans with a blue shirt, they're a blueberry. If they're wearing blue bottoms, a blue shirt and an additional blue article of clothing, they're a true blueberry.
OMG, you're wearing so much blue, you're a blueberry!
or
Hey, you're wearing blue jeans, a blue sweater and a blue shirt! You're a true blueberry.
A person in your life who is occasionally round, potentiallyirrelevant and vocalizes the fact that their in love with you, but your not and it's annoying.