Is the Bofei style in Cai Yong an official script?

Yes According to official website of Gaosanwang, Bai Fei is a special calligraphy style, which was created by Cai Yong, a calligrapher in the Eastern Han Dynasty. It was inspired by a craftsman who repaired Hongdu Gate and used a broom dipped in white ash to brush words. The main feature of this calligraphy style is that the strokes are mixed with white marks, which seems to be written with dry pen, giving people a feeling of being on cloud nine.