You should get them automatically at 30. They should show up in a separate section in the crafting log. Underneath "Recipe Level" and the various level ranges listed there, there should be a "Special Recipes" section with Dyes as its own category.



I wasn't aware of any pre-requisite before getting them. If there is any, I must have already done it before hitting 30, as the Dye section showed up automatically for me at that point.