This project is not maintained any more. I suggest you use AlreadyKnown? which does the same job, only better.

A quick and simple hack I made to ease this daily crucial choice: "should I make a new Secrets of <insert your profession here> to buy another receipe?". DontBuyIt will simply turn the patterns you already know to yellow so you quickly know if you need to craft a new Secrets to buy a new pattern.

Mostly useful at your garrison's profession buldings but works with any merchant that sells profession patterns.

Should work with any client locale though I couldn't test any besides French - please comment if it doesn't work for you.

No config whatsoever - if you don't like the color, just edit the lua file.

Septh

NB: DontBuyIt probably won't work with other addons that patch the merchant frame (Extended Vendor UI come to mind). That said, such addons usually provide similar functionality so just use one or the other, not both.