An ultrasonic diagnostic imaging system is described which assesses regurgitant flow through a mitral valve by color-flow imaging. A Doppler processor produces Doppler velocity measurements of blood flow around a regurgitant valve to identify an iso-velocity surface to be used in the PISA method of regurgitant flow quantification. The velocity measurements are used to color pixels in the colorflow image and are mapped to a plurality of colors for a color bar used with the image. The color bar exhibits distinct color transitions at one or more velocities in the velocity range of the color bar which distinctively identify an iso-velocity surface in the colorflow image. The color bar may be formed with an aliasing velocity in the middle of the bar, between a zero velocity reference color of the bar and an end of the bar, and the aliasing velocity aligned with a desired iso-velocity and used to create the color transition.
