Hilariously, Opal is apparently releasing a line of sock yarn to coincide with the release of Half-Blood Prince in the fall. I'm not surprised that the marketing of this movie extends to yarn--I'm more surprised that they haven't thought of it before, frankly--but I will admit to being puzzled by 1) the absence of Hermione-branded yarn (Ginny, Hedwig, and the Weasley twins--or one of them anyway--have a skein*) and 2) the choice to focus on character-inspired yarn instead of doing something more obvious, like house colors. I suppose they thought the appeal would be broader this way. I'm sort of unclear on what the colors have to do with the characters at all--except for Hedwig and Draco, and maybe the Weasley twins if you're generous--but this is one of the most enjoyable consumer fantasy products I've seen in a long time.
*Then again, the choices here are pretty weird too--like, why pick the scene where Ginny's in a bathrobe? (Not sold that that's what's going on there, as the label's pretty fuzzy.) Why choose only one Weasley twin? (Unless the other just isn't visible, but again, not clear.) I'd also think that Snape would be an obvious choice for a colorway (greens and smoky grays and blacks). It seems to me that whoever put this line together got a folder full of promo pics and probably attached them to some yarn that was already in development. Alternate scenario: the pictures were fed into a program that extracted the colors and the yarn was developed randomly that way. The point, in any case, is that it does not appear that a great deal of thought went into this.