Linking directly to 4chan should be marked NSFW. It's too easy to miss the domain name at the end of the link (like me).
4chan is not just /b/.
td.title a[href*="4chan.org"] { color: rgb(255, 50, 50) !important; }
Customize it to only apply to news.ycombinator.com for your choice of browser and CSS-manipulation add-on :)
(you can tell 4chan's SFW boards from NSFW by the background; the blue ones are - or, at least, should be - SFW, the yellow ones are NSFW)
Developer news / discussion sites like HN are fine, but something like 4chan.org or somethingaweful.com aren't.