Yellabone, is a slang term for a Black Female with a very light skin complexion. Sometimes they are mixed, but that is not always the case, as Black people come in many different shades.
This term is used by African Americans usually from urban areas, and can be taken as offensive if used by another race.
Elmo's weird cousin, originating from the Drawception game "Espurr is Bored." He's often portrayed as psychotic, and even has his own variation of "Tickle me Elmo" called "Pickle me Yellmo." Ironically enough, Yellmo is allergic to pickles.