Actually, I had the same problem with several of my tropical trees; including ficuses, satinwoods, bouginvilleas, etc. I took them to Harold Sasaki, who's in Wheatridge and asked him his opinion and he informed me that it was an iron deficiency! If you get an iron supplement and follow the instructions on it, it will probably help. It worked for all the trees that were yellowing, and my satinwoods are the last ones to slowly regain their green color.
--Ryan