Using the Mouassine Mosque as a landmark, keep the Mouassine fountain on your right and continue until the street widens out with shops on either side. At the point where it branches into two alleys running either side of a shop selling handmade lamps and textiles, take an immediate sharp left turn. You can follow that derb and look for the helpfully daubed word "teinturies" in spray paint and then head right. Souk des Teinturiers is also called Souk Sebbaghine. The main square for fabric dyeing is hidden down a little shimmy to the right and then immediately left, but anyone can direct you. Here you'll see men dipping fabrics into vats full of hot dye. Don't forget to look up—there are scarves and trains of wool hanging all over, in individual sets of the same bright colors.
For the best view, head into the dyers' square and ask to be led into the boutique. A dyer can show you the powders that the colors come from. A lovely bit of magic involves the fact that green powder dyes fabric red; red powder dyes things blue; and yellow powder dyes things purple. Head up the steep stairs and onto the roof if you are allowed—a spectacular view of industry unfolds, with head scarves and threads of every color hanging up to dry in separate color blocks all over the rooftops.