I think the housing refers to the chrome outlining located inside of the headlight assembly. When you pry apart the headlight assembly after heating it up, the chrome colored housing I think is screwed in. So you need to unscrew it, take it out and paint it.
Read this thread -> http://forums.nasioc.com/forums/showthread.php?t=384488&highlight=headlight+cleared
It is pretty similar to the Legacy's and it also shows pictures of the housing painted black.
Another thing: To get silver colored turn signals that blink amber, all you need to do is spray paint the stock amber signals with high temperature silver spray paint (a light coat) and that should do the same job as buying a pair of the silverstars.