When selecting cauliflower, look for one which has a firm, compact head, is cleanly white and has tight florets. Ideally, you should avoid those which are yellow or have brown spots. The leaves should appear fresh; the exterior leaves should be bright green and those closer to the florets a pale green. They should not appear wilted or show signs of yellowing. As your cauliflower ages, it may get some small black spots on the florets. Just remove them with a sharp knife. They are not unsafe to eat but do indicate that the cauliflower should be used as soon as possible.