On a kidney ultrasound some spots and red and blue what does this mean?

Doppler: A regular ultrasound shows shades of black and white to identify kidney sizes and structures. A doppler senses flow to (red) and from (blue) the probe. Doppler ultrasound is used to rule out renal artery stenosis and venous obstruction in the kidneys.

Color Doppler flow: I assume that you are looking at the us images. Red and blue are blood flow in the kidney arteries and veins as seen on doppler exam. Done to make sure good vascular flow into and out of kidney.

Blood Flow: The red and blue dots are Doppler signal, they indicate blood flow on a renal ultrasound. The kidneys are very vascular organs since they filter blood and blood flow is a normal finding. The speed of the blood flow in the renal arteries is sometimes measures to establish if a narrowing of the artery might be a reason for hypertension. Some mass lesions demonstrate abnormal blood flow.