This is a terrible picture, I know, and I'm sorry about it. =) It's the only one I could find online that shows what the boys' Weasley sweaters look like. In the movie version, Ron's sweater is the right color (yay!). However, the book makes a point to mention that Ron's sweater did NOT have an R on it, only Percy's, George's, and Fred's sweaters had their letters on it.
All of the Weasley sweaters are done in a flecked type yarn (this one is burgundy with grayish/white flecks, while Fred and George's are blue with flecks), and they all have this strange wide neck. My theory is that the neckline is supposed to be representative of Mrs. Weasley "lumpy" sweater production, as described in the books. The sweaters all seem to be baggy, also, with the drop sleeves being very low on the arm. The letters are about as wide as they are tall and resemble a Times New Roman typeface (though it is NOT, as far as I can tell, that exact typeface).
Check out Pride and Joy to see more examples of Weasley sweaters in different sizes.