Oh, by fans. I see. I don't usually read the fan replies.
I'm not sure. When she toured for her album "Electra Heart" (her second album), she wanted to be blonde because the album is a concept album, and being blonde went along with the concept. But the hairdresser who bleached her hair, ruined it, and a lot of her hair fell out. So she had to wear a wig. For much of the tour, she wore a blonde wig with prominent black roots. This was part of the album concept.
When she came back for a second leg of the tour, her hair had grown back enough that she went back to her natural brunette hair. (Performing in a wig was probably a pain in the butt. I.e., hot.) I made two video bootlegs of this concert tour, both in Philly. In one of them she has blonde hair with black roots (i.e., the wig), and in the other she's brunette (i.e., no wig):
Blonde: