Some of the data is incorrect for alchemy, where the levels indicated on this site as when the formula turns green don't actually turn green. However I'm not suggesting the site is wrong, actually i think WoW may be bugged and not displaying the appropriate color. When i was leveling my wisdom potion skill i noticed that when i hit the level allakhazam says is when it turns green, it actually turned yellow -- BUT it took 3 or 4 potions to get a skill up (acting as though it were green). Something to look into...
Besides, why do you want to know when it's yellow?