An ultrasonic imaging system for displaying color flow images includes a receiver which demodulates ultrasonic echo signals received by a transducer array and dynamically focuses the baseband echo signals. A color flow processor includes a frequency domain adaptive wall filter which automatically adjusts to changes in Doppler-shifted frequency and bandwidth of the wall signal components in the focused baseband echo signals after the echo signals have undergone Fourier transformation into the frequency domain. The mean Doppler-shifted frequency of the resulting filtered baseband echo signals is used to indicate velocity of moving scatterers and to control color in the displayed image.