With standard red/blue maps, reds represent blood flow moving toward the transducer and the blues represent blood flow moving away from the transducer. Changes in the intensity or brightness of the displayed color represent velocity differences. For example, low velocity blood flow moving toward the transducer is dark red, and high velocity blood flow is medium red.

In normal, laminar blood flow, there is very little difference between the mean velocities calculated at adjacent sample sites. With the standard red/blue, normal, unidirectional blood flow appears as either red or blue, depending on direction, or as a progression from one color to the other, if aliasing is present. In turbulent blood flow, the mean velocities at adjacent sample sites can vary significantly. The standard red/blue map shows these differences as a mixture of red and blue.