i also did a youtube video for those too lzy to read http://www.youtube.com/watch?v=P3QdSn1l-AE
basically in short.
white = standard
yellow = rapid
red = bold
However there are execptions to the rule.
If you have low durability left for example, and poor progress you would not use bold. You would use the wait option to try get a white or yellow orb to increase ure progress without destroying your item.
Bold the is the hardest method to use, and should only be used with a red orb, assuming you have the durability to work with, a successful bold syth will still consume as much durability as a failed standard syth.
Also if u get alot of standard orbs at the start (best case senario) like i did in my youtube vid, u can then use bold evan if you dont have a red orb, to try increase the quality because i had over 80% durability and 80% progress still.