During color flow imaging, which phase is typically best to capture color flow, and what color change is observed toward the black bar?

• A. Diastolic flow; brighter color toward the black bar
• B. Systolic flow; darker color toward the black bar
• C. End diastole; color remains constant
• D. Atrial contraction; color absent

Answer: (B)

Color Doppler signals are strongest when flow velocity is highest, so color flow is best captured during systole, when arterial forward flow is at its peak. The color encoding is velocity-based, with brighter colors representing higher velocities. As velocity decreases toward zero, the color intensity fades and shifts toward the neutral end of the map—often appearing darker toward the black bar on the color scale. So you’d expect bright color in systole, and a darker color toward the black bar as flow slows.