From the Super Mario Wiki
“Art, c'est vous! Are you ready to make your debut, honh?! Zee world awaits!”
Bleu is an artist with a stereotypical French accent in Super Paper Mario. He lives on the first floor of Flopside with his daughter named Lily, who secretly wants to be an actress. Bleu's name is French for blue, the color he wears and the color of his skin. His Flipside counterpart is Sacre, and together their names form the well-known French phrase Sacre bleu!.
Bleu's role in the game is to give Princess Peach haircuts in the form of a ponytail. These haircuts make Peach walk slightly faster. As Bleu states, these haircuts are hard to maintain, so whenever the player changes characters or goes up an elevator, the hairdo changes back to the old one.