why is Ariana Grande the only GIRL in this 显示 with red hair?And why did Dan choose this specific color?

Dan Schenider didn't want to have all the main characters of the 显示 have dark colored hair. He probably asked Ariana Grande in particular to dye her hair because of her character. Cat is the ditzy, bubbly character, who he believed would look best with a different colored hair along with that bright personality. I am not sure why they chose red particularly; although Cat 说 on theSlap.com that the color reminded her of red velvet cupcakes, and she liked them.

Victoria, Daniella, and Liz already had brown/black hair. Plus, all the boy characters had brown/hair. He wanted her to have red hair, so she'd be different. Plus, because of her character, he could say it was because Cat liked red velvet cupcakes! :D