Analysis:
Was "Yellow Long" one of Mary Ann Bugg's nicknames?

Astonishingly enough, no! This conclusion is the result of a compounding error. 
    Late in November 1867, the Muswellbrook correspondent for the Maitland Mercury reported: “On Saturday night last, at about nine o’clock, information was brought to the police that Thunderbolt and his woman, Louisa Mason, commonly known as Yellow Long, were at Mrs Bradford’s on the Goulburn River, the latter in a dying state”[1] (see Did Mary Ann Bugg die in 1867?).  
    Many Thunderbolt researchers have concluded – incorrectly – that Mary Ann Bugg was the woman who died at that time and, therefore, that Louisa Mason and Yellow Long (or Yellilong) were Mary Ann's nicknames. But Louisa Mason was someone else altogether and Yellow Long was that woman’s nickname, not Mary Ann’s (see Who was Louisa Mason?). 
    While Mary Ann Bugg’s skin colouring was such that Yellow Long might have been an appropriate nickname, it was not her nickname. The only references in primary-source records to Yellow Long are references to Louisa Mason (as you can determine for yourself by searching the Online Newspapers). Moreover, this sounds like the type of nickname given to someone who spent time living with Aboriginal people. Mary Ann, conversely, was sent to school in Sydney at the age of four so she could lead a “civilised life” (ironically, as it turns out!). When aged only fourteen, she married a white man and lived a “white” life until forced to take to the bush with Fred Ward in 1864. Her life circumstances were such that she was not only unlikely to bear such a nickname, she didn’t bear such a nickname.
    Yellilong (as the nickname was sometimes written) seems to have originated in a 1960s attempt to make Mary Ann seem more Aboriginal.[2] However the only primary-source reference to Yellow Long as a nickname for anybody is found in the Maitland Mercury reference.[1] 
    This is one of the many instances where a Thunderbolt writer made an error and later writers have repeated it. Unfortunately, the names Mary Ann Bugg and Yellow Long are now so closely entwined that it will be difficult to correct the secondary-source record. Future Thunderbolt writers who take the easy way out will no doubt continue to repeat this error.

Sources
[1] Maitland Mercury 28 Nov 1867 p.4
[2] Frederick Ward cuttings file at Mitchell Library, Sydney NSW