Re-stocking of colors and materials depends upon the season. In summer, priority is given to petite wools, cotton and other lighter fabrics, and vice versa in winter with heavier fibers.
For a particular color which is currently out ot stock, you can sign up to receive a notification as soon as it is available again, just click on the button "Out of stock. Tell me when it's back":
Register your e-mail address and click on "Save" in order to receive a message as soon as the desired color becomes available: