"DO YOU KNOW WHY SHE BOUGHT THE DRESS?" Owen asked.
"Sure, I know! The old man told us. "It was the dress she always sung in! 'I need somethin' to sing in!'—that's what she said when she walked in here. 'I need somethin' not like me!'—that's what she said. I'll never forget her. But I didn't know who she was—not when she come in here, not then!" Mr. Giordano said. (7.97-98)
Tabby's appearance was pretty closely tied to the identity she took on (kind of like Superman, but without any cool superpowers). At home, Tabby was a suburban mom who always wore black and white. In Boston, she got totally out of character and actively tried to be someone else. She wore a bright red dress and became this glamorous bombshell.