WOW Increasing skills

As you increase in a skill, more recipes reach a 0% chance to increase the skill (at this point the recipe will appear grey in the profession window). When a recipe turns green, a skill raise seldom occurs. A yellow recipe will raise the skill by roughly 50% of the number of iterations. An orange recipe always raises the skill 1 point (the exception to this rule being Skinning, wherein skinning a corpse which appears orange does not guarantee a skill increase, and often many such corpses must be skinned in order to raise the skill).
The chance of skilling up changes within a color band as well. For example, if a particular item goes from orange to yellow at 240 and from yellow to green at 255, the chance of skilling up will be almost as good as orange from 240-245, middling from 245-250, and barely better than green from 250-255. It is often beneficial to make high yellow items to skill up more cost effectively than orange items, but low yellow items should only be used if inexpensive (or if profitable!).