What is this manga about hair cutting?
The manga you are looking for is called "Beauty Pop".

Here is MAL's synopsis:


  Although a truly gifted hairstylist, Kiri Koshiba has no interest in using her talent to pursue fame and fortune, unlike the three popular boys in the "Scissors Project" at school. Determined to become the best makeover team in Japan, they give showy makeovers to handpicked girls. As much as Kiri tries to shy away from the Scissors Project spotlight, she finds herself responding to beauty's call