Bill Williams. Awesome Oscillator (AC) Signal Line

This indicator plots the oscillator as a histogram where blue denotes
periods suited for buying and red . for selling. If the current value
of AO (Awesome Oscillator) is above previous, the period is considered
suited for buying and the period is marked blue. If the AO value is not
above previous, the period is considered suited for selling and the
indicator marks it as red.