Alleras is described as slight, but with surprising strength in his thing arms since he’s able to use his costly goldenheart longbow. His father is Dornish and he was raised in Dorne, as he speaks with a Dornish drawl, but his mother is a Summer Islander. (IV: 6) From her, Alleras has dark skin and dark hair described as a, "a cap of tight black curls that came to a widows peak above his big black eyes." (IV: 5, 678)
Finally, the name "Alleras" when spelled backwards is, "Sarella", the name of one of Prince Oberyn’s bastard daughters. The natural conclusion, then, is that Sarella has disguised herself as Alleras so that she could study at Oldtown. This is supported by Nymeria Sand’s remark that Obara, "hates that city as much as our little sister loves it," and then Doran’s remark to Areo Hotah when he asks if Sarella should be arrested with her half-sisters: "“Unless she returns to Dorne, thereҒs naught I can do about Sarella save pray that she shows more sense than her sisters. Leave her to her . . . game." (IV: 45)